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Discussion Starter #1
I’m starting a thread for this topic even though I mentioned it in the main thread for the car. The car is a 350slc 4-speed that is I fortunately rotted, likely beyond sensible repair. But I really want to make the car run and drive to at least test the components: relatively rare 3.5, 4-speed trans, 3.46 v8 rear end. And why not at least have some fun with it too. Right?

Well, making it run gets off to a slow start, no pun intended. The starter cranks incredibly slow even with the spark plugs out. The one time I put 4 plugs in it to see what would happen, this wire going to (what I assume is) the voltage regulator started melting off the insulation.





Also, I noticed today that one of the wires on the starter solenoid looks bad.


It looks like the wire going to the solenoid is likely white, just like the wiring that melted. I haven’t proven this yet though. My plan was to get under there and start unbolting stuff, but decided to try and ground the starter before creating a bunch of work for myself.

1) grounded starter to the battery negative via the stud with no connections.

Result = No change

2) Grounded the Alternator

Result = No change

3) Removed all wires from the voltage regulator and the alternator (and taped up the voltage regulator wires)

Result = No change

It is about 42 degrees and raining. So I said “forget it” for today, but can now ask for assistance from the brain trust.

Is seems to me that the white wire either runs everything for the rest of the car, or maybe the starter solenoid. But the starter definitely turns the motor, just incredibly slowly. I first assumed the starter is bad and was going to pull it out and test its speed on the ground. Then I realized maybe I’ve just got a wiring issue. So maybe I should at least try to save myself some potential work. Removing the starter might not get me anywhere. But it might be the next step anyway.

Well, now I’m thinking that I should at least make sure there’s a solid connection in that wire that looks cut down by the starter.

Hmm... is it possible that someone messed up the wiring ages ago? This doesn’t look like a freshly installed starter though.

Heck, could the rust be causing lots of trouble in the starter internally? Is that a bad sign?

I had removed the valve covers and see there’s definitely oil on the manifold, but as I was laying under the car that was under cover in the rain, a droplet of something dripped off and landed on me. I wonder if somehow water could be dripping down and landing on the manifold and starter? Nah. It must have been oil.

Anyways, it seems strange that it doesn’t seem to be a ground or main wire issue, and there’s coincidentally this wrecked white wire.

I can get a starter. That’s probably what I will do, but understanding white that white wire cooked seems like a smart thing to resolve before moving on.



FYI:
The white wire started melting and smoking only when I cranked for a while with the spark plugs in, and after I did tests to make sure the spark plug wires were all providing spark. So I didn’t know I was melting that white wire while doing the exceeding cranking. Good news is that it does have spark. So once I solve this starter and wiring issue, I think I will have the engine running in short order. I might need to bring one of the running d-jet 450sl up from the farm in order to be able to do some side-by-side tests.




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Discussion Starter #2
Trying to plan my next move this morning.

I understand that the block in front of the battery with three big screws on it might be the easiest way to disconnect the starter wiring. Of course the battery I had in there was too big. So the first thing I did this morning is start up a car with a smaller battery to let it charge up a few minutes and then swap the batteries.

While the battery was out, I decided I should loosen up this 3 wire block terminal to gain access to its screws. But of course first crack the screws loose first. I loosened the empty coolant overflow tank and put it up there where it was accessible, tightened the Philips screws and put the battery in. Click. Nothing. I think, “hmm. I must have moved that half cut wire down there by the starter yesterday. But wait... this sounds strange. Let me fasten that block back where it was and loosen and retighten those screws.” So now it cranks slowly once again.






Interesting. I guess cleaning contacts is going to be my next move.


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Discussion Starter #3
So wire-brush-on-drill on each of the wire ends seems to get the starter running reliably, but still slow. So now I crawl under the car again to wipe wires clean and probably start looking at them again.

I’d like to get a wiring diagram to understand why the white wire to the regulator was melting when I cranked too much.
 

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Discussion Starter #4



Still slow crank.

Still need to pull another wire off the back of the alternator.

Still need to clean wires under the car.

But I anticipate I will still need to swap out the starter. But I am glad I did this investigation.
 

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Discussion Starter #5
Strangely the starter seems strong, and my understanding of the starter wiring is wrong. The medium sized wire doesn’t fire the solenoid as is expected.


I guess that makes sense:
  • huge wire to the starter
  • small wire to trigger the solenoid
  • medium wire carries some of the full battery power to the rest of the car and ignition system...
I think this graphic applies. So I think the “50” is the small wire, and the “16” is the bigger wire (and 30 is the battery hot). So it makes sense that the small wire fires the solenoid despite whatever research I’d done.




Anyway, I guess I need to compare this side-by-side with a good strong starter. I can pull one off a different motor, and give it a test. Maybe it is weaker under load, or maybe it was just poorly grounded.

Speaking of poorly grounded, I was getting somewhat intermittent behavior of zero ground. I made a video where I do nothing but attach a jumper cable to the alternator bracket and get the starter turning, but still slow of course.

So the ground is definitely a concern, but I should be able to eliminate that by running a wire directly to the starter.

Come to think of it, I’m not sure I’m seeing a ground strap on the bell housing. There’s a wire running from the battery ground to the intake manifold, but I’m not sure that’s the best place to ground the motor.





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Apply +12 volts to terminal 50 to trigger the starter solenoid. Terminal 16 bypasses the ignition ballast resistor to provide 12 volts directly to the coil for a hotter spark during cranking.

Wire the battery + directly to the big terminal (30) on the starter, and to nothing else. Jump from that terminal to terminal 50 (often a yellow wire) and the starter should crank. IF it is still slow, check the battery terminals and the ground from the battery to the engine. If they're good the starter is probably bad. If any of the connections get hot then they have high resistance and will slow the starter.

Can't help with the burnt wire without a complete diagram, but I'd suspect the alternator first if I had to guess.
 

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'80 450SLC Afro RHD Ikonengold
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It may help to uderstand full function of the Bendix as a relay, coupler and starting torque/mesh driver for motor.

When power is applied to terminal 16 as per above diagramme, it gives reduced power to the starter motor (fed through "pull" coil) to start turning it slowly - to assist meshing, it pulls the coupler lever and also brings the contacts for full power (terminal 30) to be applied to the motor and begin cranking.

Slow starter motor speed could mean that main motor contacts are not feeding the full power to the motor and power to the motor is fed only through the pull coil at lower speed/power.

Above diagramme is not quite accurate for MB, please see diagramme below.

 

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Discussion Starter #9 (Edited)
It may help to uderstand full function of the Bendix as a relay, coupler and starting torque/mesh driver for motor.

When power is applied to terminal 16 as per above diagramme, it gives reduced power to the starter motor (fed through "pull" coil) to start turning it slowly - to assist meshing, it pulls the coupler lever and also brings the contacts for full power (terminal to be applied to the motor and begin cranking.

Slow starter motor speed could mean that main motor contacts are not feeding the full power to the motor and power to the motor is fed only through the pull coil at lower speed/power.

Above diagramme is not quite accurate for MB, please see diagramme below.

Thank you. But doesn’t that diagram say MY83 for 1983?

I thought I was able to follow the picture I posted up top pretty easily with the 3 wire setup.


Edit: 50 provides solenoid power which in turn Activates the connection for both the starter motor and contact point 16, which is the bypass for the first resistor for stronger spark during starting.

Edit2: and the diagram above is for Pagoda SL and the early transistorized ignition. My understanding is that the early d-jet cars followed this wiring setup pretty much exactly. I recall studying it a LOT when I was fixing the ignition in my 1972 250 w114 sedan.


Edit3: a further look at your diagram shows a vacuum shutoff. That’s got to be for diesels. Right? W123 1983 diesels?

Edit4: I’m listening to you on the gear meshing thing, and did see that one of the two smaller wires 16 or 50 (can’t recall which) did have some voltage, but only less than 1 V when nothing was going on. I was trying to figure out which wire to put power to in order to trigger the solenoid. But here’s the thing... it makes entirely too much sense to just be this simple:


Power to 50 pulls solenoid which pops gear out and pulls the hot contacts for both the starter and 16. The power at 16 shows the bypass on the resistor. When the starter is stopped and the key turns back to “on” power runs through the resistor. Does it have to be more complicated than that? Maybe the solenoid pops the gear out before the starter gets power to mesh the gears before the starter power begins the gear spinning. Again, pretty simple, and mechanically exactly how it works. Right?
 

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Discussion Starter #10
Oh. I just watched my video that shows the starter cranking only after I move the ground wire jumper cable to the alternator (from a hose). That reminded me to mention...

I had attempted grounding the starter via one of the two studs that’s on the back of the starter. I put one side of cable on the stud (scratching the clamp around to assure i got through the corrosion), and the other end on the clamp on the negative battery post. The crank was still slow. But some doubt remained that the post was a good place to ground the starter. So some concern remained that maybe the problem was a bad ground to the starter was the problem. I’d intended to test grounding to the mounting bolts, but I pulled the starter out first. Doubt remained. :(

So I tested the starter out of the car and lightly clamped on each stud on the back side of the starter for ground. It kicked both times. So I can confirm that I did test direct ground to the starter while it was still in the car.

As for direct battery to post 30, well that’s exactly where the positive wire from the battery goes, nowhere else. Nothing really to test there. And I’m testing outside the car with the same positive wire. I pulled the whole positive harness out of the car by disconnecting it from:
  • the three terminal block behind the coolant overflow
  • the alternator (that’s the wire I’d left in the back of the alternator after removing the three wire plug of the melted wire harness).
  • the three wire guide brackets: two slide on, and one bolted to the block with an Allen bolt.
Then slid the harness under the exhaust manifold as I pulled the starter out the bottom (after removing the 19 mm bolts and turning the steering wheel all the way to the left).

I’m now confident I just need to replace the starter.

Now why did that white wire melt? Was it carrying voltage from the regulator to the alternator? If so, it could have been grounding out on the body near the coolant overflow where the wire was bent and had no installation. The high amps from being grounded there could have caused that.

I guess if power was coming from the alternator (probably battery power, not alternator power because the motor was car kin so slowly), through the voltage regulator, then the wire closest to where it was grounding out could have been the hottest, perhaps the voltage regulator was protecting the other wires coming out of the alternator. I don’t know.

Another thought... could the starter motor have fried due to this wire aching out? Maybe the white wire was grounding through the alternator, back into the starter harness through that bolted wire on the back of the alternator. Could it have somehow fried the starter somewhere along the lines?

It could have been responsible at one point in time for bad power to the starter somehow... only if somehow it was drawing down battery power. But I can’t imagine that being worse than cranking a weak battery. Right? Once that starter solenoid pops, you have full battery power. Sure, some is drained off, but it’s not like the power ever reversed itself or anything.

So I’m going to run with the assumption that the white wire not being the cause of the bad starter. Right?

Maybe the bad starter caused the white wire to melt. Maybe not.

I will pull the sheathing on that harness and insulate all the wires to assure there’s no shorting out, and plug it all back in when I get a replacement starter. I should find out quickly if there’s still something melting that white wire after the car starts. I will be sure to check the voltage and probably get the car running without the alternator at first.


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The reason I said to wire the battery + directly to the big terminal on the starter, and to nothing else was to eliminate the possibility that a short somewhere was drawing power away from the starter and making it crank slowly.

The wire itself can develope corrosion at the connections which will rob the starter of power. The problem area will get very hot.

The solenoid pull in coil, if you have one, is a distraction. The starter cannot turn the engine at all if the power is being supplied only through the pull in coil. It is possible the solenoid is not making a good connection. Easy to test; put the red probe of a volt meter terminal 30 and the black probe on the other big terminal going directly into the starter motor. Measure the voltage drop when you crank the engine. It should be no more than 0.2 volts.

If the negative terminal of the battery is connected directly to the intake manifold that should be fine, as long as the connection is clean and tight.

Do you have a wiring diagram that shows the white wire?
 

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Fonzi,

Above diagrtamme is from a 123 but applicable to later cars.
But you are right, incorrect for 73 107
See 1974 107 diagramme here


Terminal 30 feeds the power to the motor and if during cranking at least 8V is present at terminal 30 (good battery presumed) motor and contacts are right.
Bad ground or bad contacts inside bendix (higher resistance overall) will make higher voltage at terminal 30 during crank and poor crank.
I remember from my youth faults on Fiat startes to be poor bearing bushes, carbonisation and shorting between the collector tabs all causing poor crank.


2613179
 

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Discussion Starter #13
Oh. I just watched my video that shows the starter cranking only after I move the ground wire jumper cable to the alternator (from a hose). That reminded me to mention...

I had attempted grounding the starter via one of the two studs that’s on the back of the starter. I put one side of cable on the stud (scratching the clamp around to assure i got through the corrosion), and the other end on the clamp on the negative battery post. The crank was still slow. But some doubt remained that the post was a good place to ground the starter. So some concern remained that maybe the problem was a bad ground to the starter was the problem. I’d intended to test grounding to the mounting bolts, but I pulled the starter out first. Doubt remained. :(

So I tested the starter out of the car and lightly clamped on each stud on the back side of the starter for ground. It kicked both times. So I can confirm that I did test direct ground to the starter while it was still in the car.

As for direct battery to post 30, well that’s exactly where the positive wire from the battery goes, nowhere else. Nothing really to test there. And I’m testing outside the car with the same positive wire. I pulled the whole positive harness out of the car by disconnecting it from:
  • the three terminal block behind the coolant overflow
  • the alternator (that’s the wire I’d left in the back of the alternator after removing the three wire plug of the melted wire harness).
  • the three wire guide brackets: two slide on, and one bolted to the block with an Allen bolt.
Then slid the harness under the exhaust manifold as I pulled the starter out the bottom (after removing the 19 mm bolts and turning the steering wheel all the way to the left).

I’m now confident I just need to replace the starter.

Now why did that white wire melt? Was it carrying voltage from the regulator to the alternator? If so, it could have been grounding out on the body near the coolant overflow where the wire was bent and had no installation. The high amps from being grounded there could have caused that.

I guess if power was coming from the alternator (probably battery power, not alternator power because the motor was car kin so slowly), through the voltage regulator, then the wire closest to where it was grounding out could have been the hottest, perhaps the voltage regulator was protecting the other wires coming out of the alternator. I don’t know.

Another thought... could the starter motor have fried due to this wire aching out? Maybe the white wire was grounding through the alternator, back into the starter harness through that bolted wire on the back of the alternator. Could it have somehow fried the starter somewhere along the lines?

It could have been responsible at one point in time for bad power to the starter somehow... only if somehow it was drawing down battery power. But I can’t imagine that being worse than cranking a weak battery. Right? Once that starter solenoid pops, you have full battery power. Sure, some is drained off, but it’s not like the power ever reversed itself or anything.

So I’m going to run with the assumption that the white wire not being the cause of the bad starter. Right?

Maybe the bad starter caused the white wire to melt. Maybe not.

I will pull the sheathing on that harness and insulate all the wires to assure there’s no shorting out, and plug it all back in when I get a replacement starter. I should find out quickly if there’s still something melting that white wire after the car starts. I will be sure to check the voltage and probably get the car running without the alternator at first.


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Discussion Starter #14
The reason I said to wire the battery + directly to the big terminal on the starter, and to nothing else was to eliminate the possibility that a short somewhere was drawing power away from the starter and making it crank slowly.
...

Do you have a wiring diagram that shows the white wire?
No wiring diagram (yet).

RE Power to starter...
Thanks for clarifying. I think I essentially did this test with one exception: whatever connections are at that three block terminal behind the overflow. I didn’t disconnect the wires there. I realize that’s a big one, but I did disconnect all the alternator wires.

At this point, I’m getting my hands on another starter for a side by side test out of the car before I put anything back in.

Did you guys see the video of the starter outside the car I post 6? Here it is again.


It’s been a while since I’ve done a test like that. I should have my hands on a starter by tomorrow afternoon, about 16 hours from now, hopefully earlier. But since this car isn’t likely going to be running and driving by Monday, maybe I should put off this work until Monday.

My goals are to get some stuff from Jason’s shop, haul 2-3 running cars to my sisters farm for winter storage, and maybe get this 350slc into the garage over the scissor lift. The car is going to need all this before it’s running and driving, and even then, it’s still got a busted front and rear windshields.
  • starter
  • engine bay fuel hoses and run motor off a fuel pump rig to verify d-jet components work, if not, go down the d-jet rabbit hole.
  • get brakes working (no fluid in the reservoir at all). Might need to replace or crimp some lines.
  • get clutch working (pedal goes to the floor with no hydraulic pressure). Could need to replace the hydraulic cylinders. Often the slave cylinder in these is corroded. No fluid could possibly be a good thing. Got my fingers crossed.
So this one is more of a marathon than a sprint.

Here’s what I bought based on pics:


If I decide to actually drive it for any significant amount of time, I’ve got some front and rear glass I can install. I’ve already removed most of the “I want to appear to be more than I am” stuff: 450slc and 5.0 badges, rear spoiler, AMG front lip, BBS wheels, chrome on the sides and wheel arches. It looks better already IMO.

Anyway, I will report back probably tomorrow on the starter, and hopefully have the motor running by Monday-Tuesday. I should figure out if that white wire continues to be a problem.




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If the white wire is in a harness it may well have melted into some of the other wires. I would open the harness up and make sure everything is properly isolated before I apply power to anything. Otherwise you could have a much bigger problem on your hands...
 

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Fonzi,

I'm just catching up on this thread - it looks like your alternator is a later model with internal regulator. '73 had the external regulator near the right headlight. That may be the reason your alternator wire has a a splice and drama with that burnt white wire.
 

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Discussion Starter #17
Fonzi,

I'm just catching up on this thread - it looks like your alternator is a later model with internal regulator. '73 had the external regulator near the right headlight. That may be the reason your alternator wire has a a splice and drama with that burnt white wire.
Did you see the thing by the right headlight in my earliest videos (or maybe pictures) that sure looks like an external voltage regulator?

Was there something about the alternator that makes it look like a later model one?

I wonder if you are right and they put the wrong one in the car because it’s a euro and they bought the wrong part.


If the white wire is in a harness it may well have melted into some of the other wires. I would open the harness up and make sure everything is properly isolated before I apply power to anything. Otherwise you could have a much bigger problem on your hands...
Yep. In the plans for sure.


Edit:
I was successful in getting two starters and the fuel pump rig to get this car running. I also got @dgosh28 ‘s old 450slc 5.0 out of Jason’s shop where it was penned in, and also got the 500sl project out of the weather and into Jason’s shop where it will get put back on the road. It’s right in front of the lift for transmission and tri-y installation. So happy about that!

No off to the wife’s work holiday party. Both the 450slc 5.0 will probably go to the farm for winter storage in the next few days. I need to get the 350slc inside the garage for winter work and to clear the driveway to get the kids a new basketball hoop for Christmas (or sooner). Making progress!
 

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Discussion Starter #18
Well, although unplanned, I put a starter in with the same wiring from the 350slc, and I got the same behavior, but I decided to run the starter just like I was running them outside the car. My battery is running weak and now is charging. Voltage drops below 10v (down near 9 actually) when cranking. Since I am just dropping the small wire to the battery positive, rather than using the key, I can see that the negative contact started smoking where the cable is clamped to the battery terminal. So that surely needs cleaning. I’m not sure if I get smoking when the jumper cable is connected to the negative. I can check later.

So I don’t know whether there’s an issue with my positive wiring, but out of the car it didn’t behave differently than the other set of wires I’ve got that is definitely different with no wire for the alternator. That could have come out of a w111 with a generator. So I’m going to have to look at one of the 1973 v8 cars to see what is correct. That’s the main reason I re-used the original wiring for this test.

The motor seemed to turn really easily from the 27 mm nut on the crank pulley. So it doesn’t seem like it’s seized to me.

I’m definitely going to make sure I’ve got strong battery for the next test, maybe even run with jumper cables from a running vehicle to make sure power isn’t an issue.

A busy afternoon and evening is starting now, and I was hoping to get the car moving on starter power because I’ve got to move the car if I want to move my SLC convertible to the farm storage.

Anyway, this thread seems to have good reason to exist now that replacing the starter hasn’t solved the issue.

I will maybe load videos later.
 

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Discussion Starter #19
Took this video earlier today. Maybe tonight I can clean contacts, put the battery back in that’s been on a charger since this afternoon (registered 50% charged on my auto charger, so wasn’t complete toast), and hook up jumpers to my Honda Ridgeline I parked right in front of the car.


Not relying on what I believe are good batteries (able to easily start other cars), and cleaning the grounds seems like what I should have done first, not last.

... But I rarely do things the easy way.
 

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Discussion Starter #20
Here’s cranking last night after cleaning grounds and charging the battery. Bolts drop to 10 when cranking. I haven’t tried jumper cables to a running vehicle yet. It’s rainy here, and I haven’t gotten the car into the garage yet.



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