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Smog help! O2sensor, air injection, egr

4K views 61 replies 9 participants last post by  Jbridges154175 
#1 ·
Man o Man where do I start?

First you should know that this is the first non-Chevy I have owned and only performed basic maintenance on them.

The car will not pass smog. Running way to rich. I know I have a code for the bank 1 o2 sensor. I also have a code for the egr. Traced egr problem to the switchover valve and pulled a code for this as well. The guy at smog said my air injection was out. I know the egr switch over, the upshift delay, and air injection are all tied to fuse 7. Gonna check that today when I test the o2.

Questions
Can the egr and the air ejection be effected by a single relay as well?
Does anyone have a layout?

Since the car is running rich does that mean the o2 sensor should be anything but .9 hm assuming it is bad and I am assuming it's bad.

If I Check voltage and hms at the connector to the sensor and the computer they read the same if the wiring is ok right?

Also i need instruction on testing every switch, valve and sensor and other possible causes. Also How to test the wiring to each.



Below is more indepth about car and situation.
It has important info that should be read.

I bought a 95 e320 from my mom and her husband a few months after I got out of prison. I felt it important to add the prison part so you understand where I am at financially and how important it is I have a dependable ride.

The car ran fine at go outside of a leaking transmission when the car is in park. Then I started noticing some loss of power, by no CEL. When I took it to smog so I could transfer the title, it failed horribly. When I pulled out of the smog place the CEL lit up. Repair shops are way to expensive for someone fresh out of prison, so I went to doing research. I found out from you guys how to build my own tester and about the wiring harness junk. Ran codes and boy did I get a lot. It was a bit overwhelming. Then I checked the wiring. About half of them look brand new the others are old for sure. I will upload pictures later. There is some bare wire inside loom that I can see. A couple days after this I started blowing fuses. A couple more days and my fuel, oil pressure, temp, and rpm gauges all went out. I parked the car at my then girlfriends house and it wouldnt crank. Wouldnt even try. Now it had issues with the neutral safety switch so I tried in neutral. Still nothing. I put it in reverse and the reverse lights came on. I came home to do research and found that my problem was most likely fuse 5. I havent completely paid for the car yet and because smog it is still in my Moms husbands name. He blamed me for the problems and had it towed to the shop. This on Christmas and the day before I was set to go on a cruise. The mechanic kept it for three weeks. At first he said he couldnt get the transmison to register. I informed my parents about the neutral safety switch but they did relay this info. He ended up bypassing thenuetral safety switch and im guessing the anti theft lock out because they run on fuse 5 and the gauges that are also on fuse 5 are out. He says he couldnt fix the o2 because the computer was fried. The thing is we took it to his smog guy and when we left the CEL came on. Now if the ecu fried then why did the light come on? I pulled codes and only got two. Either 2 and 3 or three and 4. The last was the lambada control. I know that can be the o2. I am going to drive it a bit today to get the rest of the codes back. I knew about the neutral safety switch and I just staryed learning from scratch but the mechanic said he had to call a transmison specialist over to tell him. Doubtful. He says he checked fuses but I could hear humming from the fuse box. My Windows now wont roll down. Today is the first day I have had access to the car and maybe the only. We are doing this without moms husbands knowledge. He wants to retire it. I suspect a hidden agenda on his part and the mechanic pretty much is shady. I need this car and at this point it's a matter of pride. I know there is something not right. I plan on making this car my baybe now.
 
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#2 ·
if your engine wiring harness is bad (and *ALL* 93-95 M104 and M119 engines came with bad harnesses), all bets are off until that's replaced, all sorts of random crap will keep happening. the whole main upper harness for the engine is all one part. also, the electronic throttle needs to be updated too, if its not already a replacement part with a date code 1998 or newer. there is also a lower engine harness, but its quite simple, and just involves the starter, oil pressure sensor, and a couple other relatively minor things.

once the wiring is sorted out, THEN you can start troubleshooting any remaining problems
 
#3 ·
Mr Bridges

Welcome to the forum. The knowledge base here is deep and the collective membership will help you in any way we can. LeftCoast is spot on regarding the the harnesses and throttle actuator. Sadly, if these items aren't replaced, there is no way to get the car to perform as it should.

If a family member disagrees, they are misinformed. The problem with the harnesses is the soybean based wire insulation (a very well documented problem) which breaks down over time, first cracking, then turning into powder. As an example, in September, I bought a 34,214 mile 95 E320. Always garaged always dealer serviced. All harnesses and the throttle actuator already replaced.

Start searching eBay. You can probably find post 1998 of each in the neighborhood of $400-450 for the two.

Keep us posted and good luck

Again, welcome

Jayare
 
#4 ·
Thanks

Thanks LeftCoastGeek and Jayare (is that a play on JR as in Junior?)
This is my first post, however I have been reading this forum for awhile now as well as the peach parts one. I see you two guys quite a bit. You guys are very helpful. Through y'all I have learned about the wiring harness issues, how to test the EGR valve, the little tid bit about sensor 5 being the culprit for my no crank, and much more. I've been researching for awhile now.

Now for the but....

In my current situation I do not have the option of getting a new wiring harness. Atleast not right now. I have checked and found some really cheap ones and also ran across a thread about running your own wiring. I am seriously considering building my on ECU from the DYIEFI.org open source sight. I have a computer science background so I believe this to be possible for me. But all that will have to be down the road.

As of right now, I have to get this car to pass smog. If I don't get it done soon, like this week, I will lose the car for good. I am considering tracing some of the wires and wrapping tape around them and heat shrinking the tape as a temporary fix. I know I know, that is horrible but its all i can do right now and should stop it from grounding out.
 
#5 ·
this is a rather complex engine with sequential fuel injection (each of the 6 injectors fires on its own timing), crank position sensor, variable camshaft, with a camshaft position sensor, air pump air injection for smog, digital distributorless ignition, electronic idle speed and cruise control integrated into that electronic throttle, all sorts of other engine sensors, and to pass smog ALL of that has to work perfectly. you MIGHT get the engine running with a DYI ECU, but you'd be completely rewiring it, it would be an ungodly mess, and the odds of it EVER passing smog are between slim and none. there's likely over 100 wires in that wiring harness, which means 200 connections, all have to be perfect. good luck finding enough different colored wires to create a replacement harness.

here's the main engine wiring diagrams
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/24072001.pdf
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/24072002.pdf
and the CC/ICS throttle,
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/2430200.pdf

if your car has ASR, then you have this throttle instead
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/2430100.pdf
and the ASR system,
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/2442200.pdf

starter/generator/battery:
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/2415100.pdf

engine diagnostics system
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/2407700.pdf

automatic transmission control,
http://new.freescruz.com/.priv/W124/w124CD1/Program/ETM/2427300.pdf

and there's lots more thats also under the hood, like ABS, lighting, etc

you can't bodge these cars.
 
#6 ·
There really isn't any good news for you. These are great cars, but they are also old and complex. Stuff will need to be replaced and there aren't too many cheap work-arounds. The First E320 I bought was sold cheap because a mechanic, trying to help the previous owner, tried to re-insulate the upper wiring harness. What the mechanic should have done was buy a used one for $300 rather than spending hours upon hours trying to wrap an engine harness, but he only knew what the harnesses cost new $$$. But if $300 is too much for you, then it may be worth your while to go at it with electrical tape. It will be A LOT of wrapping. If it continues to short, it will eventually fry your ECM.

Another option is to go to a local scrapyard and pull the harness from another MBZ. There is a decent chance it will be an updated harness. You can search on here at to how to tell if a harness is updated. I would guess a junkyard is going to charge you less than $100 for a harness (takes about an hour to remove). Some members here regularly grab parts from yards and can tell you how much it will cost (and maybe even some good leads on where to find them). If I'm not mistaken, harnesses from other models may work too ( similar era C class maybe?).

Once you get that squared away, you can tackle the smog issue. While it is possible the harness alone may cure it, you may be looking at other expenses: $75 for an O2 sensor, $100 for a MAF, $200 for a cat, coils and plugs ($200). Hopefully, it won't need any of that, but some things will simply cost you money.

Lastly, and our CA members can chime in, but I think there are several income-contingent SMOG assistance programs in CA. You may want to look into those as well.
 
#7 ·
if a car is flagged as a gross polluter, AND you've spent over ???? dollars on trying to repair it, and you're low income, you can get an exemption, but I think its only for a year or two. they really want old dirty cars off the road, especially in places like LA which is naturally a smog basin. I remember flying over LA in the mid 70s in a private plane at 8000' and not being able to see the ground at ALL for 100 miles.
 
#8 ·
re harnesses, I believe 94 and 95 use different harnesses as there's some wiring changes. i see a change on the diagrams for up to 8/94 and after 9/94 relating to the camshaft position sensor, knock sensors, and ECT (engine coolant temp). 9/94 is probably the cut-in date for 1995 model year cars.
 
#9 ·
Today's progress UPDATE

Today I went and got a new o2 sensor and multi-meter. I was betting the o2 was bad and if it wasnt would just return the new one.

Development
On the way, I noticed that the gauges were on and the buzzing from the fuse box had stopped. When I left the first parts store, I decided to try and crank the car with the key instead of the button that the mechanic installed. It cranked right up. This to me confirms that it was/is a fuse 5 issue. When I got to the next parts store and tried to crank it the same way it wouldnt crank, and the gauges were out again. Had to use the button.

Plan
I didnt have time to check the fuse, because the sensor took priority. I plan on checking the fuse is not blown and making good contact. If that doesn't fix the issue then I think my best bet is to assume a short somewhere. If that is the case, I am going to unhook all wires from fuse 5 and replace them one by one (unhooking battery before each connection). Hopefully this will tell me where the short is.

Questions.
If there is in fact a short somewhere wouldn't it blow the fuse?
If its possible to short the whole fuse out without blowing it, then I should be able to see a drop in voltage if I test at fuse connection right? Or a spike in the ohms/amps right? I'm pretty much just making a educated guess on that one.

o2 Sensor Update
I checked the ohms by undoing the single green wire connector, inserting a single stand of wire inside one, and then closing the connector. I am not sure I used the right setting for the ohms but is far as I could tell it just moved the decimal over each setting. I came out with a reading of 0.5 hms. Normal range. I knew the sensor was bad at that point because it was running rich as confirmed by the SMOG test, the low mpg, and the fact I could smell the gas. Ohms should have been closer to 0.9. I also noticed that whoever installed the old o2 had used but connectors like you would use on speaker wire to splice there wire. It was original fit. I'm not sure why they did this. In my uI forgot to check the output for the two white heating wires on the 3 part plug coming from the supply (ecu). I will do this.

Problem
After putting the new sensor on and cranking the car, I noticed some slight rough idle and a little hesitation on acceleration. Could also hear a vibration at exhaust tips. To me it acted as if the EGR kicked in or it is now somehow runnin lean. Spoke to a mech buddy of mine back home and he said it sounded like I didn't tighten down the sensor enough and had a exhaust leak. He also suggested to use stop leak but I read that it was advised not to and the sensor had some green stuff around the thread to stop that from happening. The pipes and engine had also cooled down before I could get the new o2 on. Read that it was supposed to be done hot.

Plan
To try and tighten the sensor more.
Test sensor output and output voltage from ecu.
Also see if the ERG does infact have vacume.
Clean EGR pipe.
Check spark plugs
Clear codes
Recheck MAF now that the o2 should be working

Questions
Any Suggestions?
Does the egr even kick on during start up? I know its not supposed to on cold starts and when under stress, but what about when the are is not cold?
Since the o2 is now good and it hasnt been for awhile can it just take awhile for the computer to adjust?
Since the computer is now taking in the correct info from the smog, changing the fuel ratio, can this make problems that were hiddin somewhere else come to light.
Can the egr and/or air pump be causing these problems now that the o2 is right?
Can clearing the codes help?
ANY SUGGESTIONS.

Side note.
I suspect some deception on the part of the mechanic. The fact he didnt even attempt to address the fuse 5 issue. The fact he said the computer was out when it clearly isnt. The fact that he claims not to know about a neutral saftey switch and didnt think to try and start it in nuetral. The fact that I knew these things and they turned out right.

But I cant escape the scary thought that what if he really is just not a good mechanic. What if he really somehow did drop the ball on all these. What if he adjusted the air/fuel ratio to try and compensate for the computer or anything like this. Id be screwed.

The car has been running pretty good since it left his shop.
 
#10 ·
there are no adjustments on air/fuel mixtures on HFM-SFI cars, its entirely controlled by the ECM and fine tuned via the inputs from O2 sensor.

O2 sensors can easily be tested with a volt meter, but if they are out of spec, the ECM would register an appropriate fault code readable on the diagnostic panel near the battery.

IF YOUR WIRING HARNESS IS BAD, THERE IS NO POINT IN DOING ANYTHING ELSE UNTIL YOU REPLACE IT WITH A GOOD HARNESS. your wiring is crumbling inside those black covers, throughout the harness. stuff isn't just shorting to ground, circuits are cross connecting randomly to each other. ALL BETS ARE OFF.
 
#11 ·
Thanks again

Sorry guys. That last post was suppose to come in right after the one yall commented on.

Dude LeftCoast. Thank you! I have been searching and searching for all the systems. Now I just have the very long task of understanding some of these wiring diagrams. They are unlike any schematic I have ever seen. Search for pictures that point to where they are exactly. And find the test procedures for each. Will also make finding any electrical leaks easier to find. That is really a big help. I understand the basic functions of some of the things you listed. egr, timing, distributer, air injection. Some of the stuff however I have never heard of. This engine really is suprisingly complicated.

I think I can take care of a good portion of the electrical issues I am having, for the purpose of smog, just by figuring out what is going on at fuse 7. I have a basic plan for that. Test the fuse port itself. If power is supplied, check each line that feeds of that. Really not looking forward to tracing every wire but it has to be done. I havent gotten that chance to really study the diagrams yet, but wires that actually carry signal wouldn't be fused would they? For instance the green wire that send signal from the o2 to the computer wouldn't route through the fuse box would it? My fear is that I trace one of the wires and the jacket crumbles. That would be a huge deal since the resistance has to be exactly right. Power isn't really so much a big deal as far as that goes. For the life of me I cant figure out why they would mix no critical systems like the gauges in with the same fuses as systems like ecu and air injection. See any problem with buying a seperate fuse line for no critical power as long as i get the amperage right? or do they do that to make diagnosis easier?

In no way do I believe that I could possibly tackle the DIY ECU anytime soon. That is a hopeful long term project. My plan with that is to use an easy system. Say the air injection system. Shouldnt take that many paramaters to know when to activate it. Plus i need the ecu working like factory condition because I would need the DIY to learn form the factory. Either way thats later.

Tomorrow I pull codes I have now. Test as much as I can. deal with fuses 5 and 7. (if i am not mistaken the radio runs off one of these. That might be an issue considering my radio is fine. Hell my air works too) Clear the codes. I have to pick up my check 30 mins away so I figure that drive will be enough to pop any codes and compare before and after. If I have time then I will work on figuring out a solution to the wiring issue. Why couldnt they have made the harness connect to the damn ecu with each system having its own connector. why have one big my bad 2 big connector.

Anyway thank you guys for your help. any testing procedures for any of the efi systems would be much appreciated. Starting with the most likely. im off to the wonderful world of wiring diagrams.
 
#13 ·
Also in order to get assistance from the state you have to have the car two years, and be low income. The car isn't in my name remember? And the person's name it,is in makes over 300k a year. He isn't getting assistance. Most I could get would be 1000 in a couple months. No I don't have 300 to spend on wiring, not even planning on buying the harness anyway. I am going to run my own power one I understand the print. The only thing I don't know about is signal wire.
 
#14 ·
Today update.
Fuse 5 was just blown. Changed it with the one for the mirrors until I can get more. Car starts up with key, still oddly needs to be in neutral though. O the drama that one fuse caused, if you only knew. Good news is that proves I was right the whole time and the mechanic wrong. It's gonna by me some time. In fact it proves everything I said right and everything the mechanic said wrong.

I took the car to smog today. The car was running great after the o2 swap and resetting the ecu. It had more power than I ever remember it having and got almost triple the gas. But it went the exam opposite this time. Well it wasn't as bad but instead of running rich I'm running lean. The damn CO didn't even measure. Kinda good though, because I don't have to worry about it going back to a failing measure when i get the fuel mixture right. Here is the problem. Before I reset the ecu I disconnected the MAF as a test and it had almost no effect on the engine, so after I failed I though the MAF. But now when I take it off it almost died like it should. The EGR is still down but it would run during the test because the out the engine under stress while doing it. I could just stick the egr open during testing and probably pass but I want to do it the right way so I know the car is balanced. And plays I want to try and pass without get because I want to delete it. The air injection is still out but only though it activated During cold cranks and if there is to much oxygen in the first place It would return the gas would it? I'm kinda lost. Maybe vacuumed leak, maybe and injectors. Idk. The CEL isn't picking it up either. There is water coming from rail pipe now and white smoke was coming from car after test and ran a little hot
 
#15 · (Edited)
Let me see if I can help you out here. As LeftCoastGeek pointed out, if you have a bad harness and bad throttle, your attempt will be all wasted. The best source for an engine harness is from junk yard. If you can find one in your area and they have some E320s, you could find those nice updated harness for around $50, such as from LKQ. For late 1995 E320s, they use a harness with the last four digit 2933. You can identify this easily by looking at the connector on top of the water pump. If you see two connectors, one with two pins and one with one pin, you have the older harness used for 1994 and early 1995. The late 1995 harness is much harder to come by in the junkyard. You can also try to get one from eBay for about $200 to $300.

1995 Mercedes Benz W124 Late Engine Wiring Harness 'Made in 2001' 1244402933

1995 Mercedes Benz W124 Late Engine Wiring Harness 'Made in 2001' 1244402933 | eBay

1993-94 Mercedes Benz W124 Early Engine Wiring Harness 'Made in 2003' 1244405632

1993-94 Mercedes Benz W124 Early Engine Wiring Harness 'Made in 2003' 1244405632


Throttle body could be rebuilt as DIY, not too hard. If you can get smooth idling, you might be able to get by with current throttle body for a while. There is a date code on the throttle body to verify if you have an update one or an old one. The date code should be 98 or later. Most throttle body are not replaced, unlike engine harness. If you remove the throttle body (not recommended because the wiring could be all messed up) and open the cover, you will be able to tell if insulation is good or bad. Don't touch it for now to avoid upsetting the wires if you do have a bad insulation throttle body.

Good luck. Also, the price of the Hot Film (MAF) is quite affordable in junkyards.

jftu105
 
#17 ·
Of course, there would be updated throttle bodies in some E320s, but the percentage of E320 with an updated throttle body vs updated harness is relatively lower. During my junkyard hunting period (no anymore), I was able to pick many sets of harness (over 10) but only a handful of throttle bodies (2 to 3 at most). The throttle body sometimes would still work despite the bad insulation if you don't upset them. It is like cookies in a box if you don't crush it. I had to replace all my throttle bodies for all four E320s I have owned (one sold), 3 of them had updated harness but none of with updated throttle bodies. My friend's E320, with 40,000 miles when he bought it, was the same. I replaced the throttle body for him.

jftu105
 
#18 ·
I swear I thought I posted this yesterday but apparently not. I am a low voltage electrian. I assure you I am well capable of determining how serious an electrical issue is. I am pretty sure I have new harnesses. Just looks like one was left in the rain. Jackets are decent but the connector are in shape. That part is not a big issue and not causing my main problem.

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#19 ·
The only way to verify eco junk wiring is not the cause is to verify the build dates on the harness tag (behind battery splash shield) and the throttle body

Harness build date should look like F.D. xx.xx.xx

Throttle body build date should look like xxMxx

Report back with those dates and we'll go from there. Until the eco junk bug has been completely eradicated, these cars cannot be troubleshot.
 
#20 ·
Electrical I know. I'm just learning mechanics. I haven't checked throttle body yet. Would love to clean the intake and valves this week but they didn't have the gaskets. I was going to test and clean injectors and throttle body tomorrow but haven't looked up how yet. I am taking them off to clean them because I don't want all that junk getting sucked in my motor.

Updated.
I didn't do much today. Really nothing. I want and checked the new sensor.

At idol It's good. 0.8 was the higest it got and 2 was the lowest. Seeming to average are .5 or .4. I left my my multimeter hook up and connected a vacume to the egr. It really didn't make the impact I was hoping.

Giving it has is where I am at a loss. When I give it gas it drops below .1. It gets to .o2 at 2000 rpms without egr and .4 with the egr. And it stays pretty steady. And then if I hold the gas to right before you let off completely it gets all the way rich. The MAF did pop today so hopefully I can just clean that while I do the jets. Also going to check for vacuume leaks

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#21 ·
Guys come on now.

Sbaert, I appreciate the info on how to find the date of the wiring harness. I do.

However even if it is the eco junk, by the way you guys are talking about it I seriously doubt it, but even if it is, I AM NOT REPLACING it right now. Most wires are in good shape. The ones that arnt I going to rewire.

As far as trouble shooting not working, I think I have done a pretty good job so far. A new harness is not an option right now. I mean I can't even afford new gaskets or have the time to wait on them to be shipped. My wiring issues are due to human error. In fact I'm willing to bet that is my problem right now. Human error from someone who got it in their mind it needed a new wiring harness and didn't even consider other options (the mechanic who insisted it be junked)

Left Coast did it right. Seen that I couldn't or wasn't going to do the harness and still assisted.

If y'all truly want to help then help me find diagrams, tutorials, specs like the amperage a egr switch over valve works, parameters of when it activates, stuff like that is what I need.

I need to know stuff like when the tub from the egr goes into the manifold where does it go from there. What controls the amount of air vs the amount of gas from egr goes into the cylinder. It's DI so how does it get to each cylider.

How do I check the distibuter, coil pack, and ignition.

What's the best way to check the fuel system without a pressurized.

How do I check the blow off valve, is the the same thing as the PTCs.

How can I read the variables the computer reads and the ones it sends out? Like what it says the sensor is detecting lean or rich? What about what the computer thinks load is, what it says timing should be, when it picks up a knock from the knock sensors, when it thinks there waz a misfire.

How can I check how long it is telling the sensor to open? How much air to bring in.
At what rpm, coolant temp does it say to increase idol.

What should idol be?
How do I do the load test or the test that tells you the fuel ratio. Going to take my multimeter back today and get the better one.


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#22 ·
I guess I am going to have to start making videos. I wanted to anyway. It's just this is the first time I've done any of this and I'm not very smooth. But that might make it better.

I'm def, going make them to when it comes to rewiring. I don't get you guys on that. You will tear down a whole car and rebuild it. So complex conversions and swaps. Understand in depth complex working of the engine, but your scared of a little rewiring and testing. I promise it's not that hard. He'll you can use 18-2 for just of it. All you have to do is figures out what the range of amperage, voltage your component needs for power and choose the right gauge, type, and fuse and send it. Everything I've seen so far takes 13 to 14 volts. If it's not just super high amperage then outside high heat plenum ratted 18-2 is fine. I've seen that crap hold up data cables that were sagging from heat at a steel mill. The only wires that has any potential to be a problem is the ones that feed data.

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#23 · (Edited)
That particular engine does not have a distributor. However, the ENTIRE ignition system is deemed disposable and consists of 3 coils, 3 coil to plug boots, and 3 spark plug cables and 6 plugs. The coils, boots and wires last on average 100-125K miles while the plugs should be replaced every 25-30K miles.

The ONLY suitable plug for that engine is Bosch F8DC4, nothing else. No exceptions.

Idle is under full computer control, and cannot be adjusted in any way. Normally at full operating temp should be around 650 rpm.

I highly, highly suggest you contact forum member Nobletruths, as he stocks 2nd harnesses and throttle bodies that do not have any eco junk disease.

One more thing, always replaced the throttle body gasket with a brand new one whenever R&R'ing the throttle body to avoid vacuum leaks.

I do NOT recommend rewiring the throttle body, as I have never come across one that lasts the long haul. In addition, you must have the proper gauge wiring. And the throttle body uses 2 different strands inside the loom that need to have a certain amount of twists in order to work 100%.
 
#25 ·
Thanks guys. Jayare a few of those guys were just guessing. Like it didn't burn or fuse must be good. I really am thinking about making videos about basic wiring.
There is basicly two catigories of wire you are dealing with. Wires that carry signal and wires that Cary power.
Power is easy. Get the right amperage and right voltage to the components.
Sometimes order matters. Not all logic is programming. There us some logic to some stuff in power. I'm hoping that component list LeftCoast provided has the voltage and amperage tolerances for them.

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#26 ·
all Mercedes wiring is metric, not AWG, the gauges are given on most of those wires as like 0.75, meaning 0.75 mm^2, the color codes are in German, where SB is Black, most of the other colors are self evident. GN is green, GR is Grey.

On these sorts of cars, the power wiring tends to be switched (there's your logic), and the signal wiring tends to be analog/linear.

the wiring diagrams have nothing about voltage or amperage or any other sort of specifications, they just show how stuff is wired. A bunch of stuff shows DIN signal codes, where like 30 is unswitched power, 15 is power w/ ignition, 31 is ground, etc. Mercedes hews pretty close to the DIN spec for this, here's a reference: https://en.wikipedia.org/wiki/DIN_72552
 
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