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Ugh - wiring....

6K views 101 replies 7 participants last post by  Patman1 
#1 ·
I was changing the motor mounts on my car this weekend, and saw a piece of tape hanging down near the transmission. I yanked it. What a mistake. I saw it was the wrapping on the wiring harness going to the transmission, and when I pulled it, it knocked the insulation off a bundle of about 8 wires. Of course, the insulation is like powder anyway, but I shouldn't have bothered it. I was in horror when I saw the bare wires all in a bundle.

I carefully pulled each wire and wrapped some electrical tape around them, being as careful as I could, but it was impossible to do a good job at the ends where they go back into the bundle. Car seems to run fine, but I am afraid of running in the rain. It is rainy today, so we'll see maybe.

Not looking forward to a harness replacement, but I guess that is what I am going to need.
 
#4 ·
#5 · (Edited)
You can always use this until you source a harness:
Amazon.com: Gardner Bender LTB-400 4-Ounce Black Liquid Electrical Tape: Home Improvement

Harbor freight sells it as well as true value if you have a store nearby. Give it a coat, let it dry good, give it another coat, etc, til you have a good thickness built up on it.
Thanks, George. I have some of that and thought about trying it there, but I think there are too many wires and the tight space is an issue, so I didn't think it would work well. I did use it on the split wire that feeds my throttle body and it helped, but ultimately I replaced it because it still acted up in the rain. Although part of me is now wondering if it wasn't the transmission wires that were really the culprit after seeing this mess.
 
#7 ·
It would quit idling, and also the speed would not control - when trying to keep the speed constant it would accelerate or decelerate alternately. I think it was the throttle valve - the problem did go away when I changed it.

As it turns out, it seems that there is a separate wiring harness for the transmission, which can be had new for about $150. I will verify that it is the right one for my car and order it. Doesn't look too hard to install, only 4 ends on the harness, so I will try to do it myself. Meanwhile, I have parked the car, not that it was acting up, but it is raining at the moment and I don't trust my tape job in the rain, and I would like to not be stranded somewhere.
 
#10 ·
In looking around at the main harness wiring, it too appears to be in bad shape in places. I am not sure I want to sink another $1500-2000 into this car.

I will change out the tranny harness and go from there I guess. The new harness should arrive next week so next weekend I will change it out.
 
#12 ·
Well I definitely have a bad transmission harness. The main harness has yet to be determined, but it looked like there were cracks in the insulation at one of the end point plugs. I will have to look at it further.

The transmission harness, the insulation falls off the wires like dust, and the corrugated outer tube crunches like cereal between your fingers.

My car is a '96, which is mid 90's.
 
#13 ·
Sorry I misread. I got confused with all the talk about 2000 models.

I have the same issues with failing engine harness. My whole harness has not been changed...just bits and pieces!

Someone (maybe Doing12volt)?? used to rebuild them once. Don't know if he still does. He did a great job too.
 
#15 ·
Sh!t. You don't have to tell me about it.

These stupid tree-huggers are the root of all these problems. Now we have to spend more money fixing this issue and where does that money come from? They have to make new harnesses, I have to work longer hours and so the overall carbon foot print is way more than if they had just kept those non-bio harnesses.

That is why I don't buy into anything these hippies try sell unless it's way cheaper than what I currently have. I'd put an oil drilling rig in my backyard if there was oil under my property. Then I would bitch-slap all the hippies that try to tell me otherwise.
 
#16 ·
Do sink another 1500$ in this car. I did. I replaced my engine harness and the small ignition harness one year ago. I found a harness on ebay for 1200$ (new), and I installed it myself. It took a full day, I also took the opportunity to change my spark plug wires, ignition coils and OVP relay. I have been driving my car for 1 year problem free now.
 
#17 ·
Well, I changed the transmission harness today. What a pain. I ended up cutting the old one because it was jammed into areas that were not particularly accessible and I routed the new one a different way. Then you have one part that attaches onto the starter motor, which is nearly impossible to get to.

But got it done, and went to start up the car and test her out.

Car won't turn over. I think I disturbed the main engine wiring harness, and likely there is some short going on there. Which means I need to change the motor wiring harness now. And hopefully that is the problem, not really sure.

Grrrrrr.
 
#19 ·
Possible. The harness only has 4 connections. One up front, one on the transmission, one on the rear of the transmission, and one other that is just a grommet attachment. I believe that one gets attached to the starter motor, which is where I attached it. Very very difficult to get to. Plus I could not see exactly where that part of the original harness went to. I will have to go under and have another look.

However, I know that I disturbed the main harness at the front of the car, and the insulation dusted off, and those wires are likely touching each other.

This wiring is the most amazing thing ever. You just touch it and the insulation instantly turns to dust and falls off.
 
#21 ·
So, does anyone know how to get to some of the places the harness goes to without disassembling the whole engine? In particular, there seems to be 2 connections under the intake manifold - I can barely see one and can't see the other, and fuggedabout actually reaching either one.

Anyone who has done this job before, I would welcome any insights.

If not, I guess I will tow the thing to my local german car mechanic and let him figure out what I have undone so far and then install the new harnesses (harnii?) at what I am sure will be an exorbitant cost.
 
#22 ·
Those connections are a sumbitch, but it can be done. I remember when I did mine it seemed like I pulled everything but the kitchen sink off of it, but in hind sight, you might try removing the serpentine belt, then undo the bolts holding the power steering pump to the engine. You can move it out of the way with the lines attached and get you hand underneath the manifold. I will confess though, when I did mine, I had an intake gasket on standby, and I ended up unbolting the intake manifold to get at some of them. Not terribly difficult, but very time consuming. Try removing the PS pump, its not hard and can be done fairly quickly.
 
#24 ·
Have made a little progress changing my wiring harness. Between rain storms, blazing heat and being too busy, I haven't had much time to work on it. Plus I ended up ordering a long-handled pivoting head ratchet to get to the bolt holding on the manifold support, and that took nearly 2 weeks to get here from harbor freight. So I finally got the manifold undone, although there is no easy way to actually remove it from the car it seems. That's OK, since I just need to move it around and out of the way to reach certain areas. I re-installed the piece of the harness that goes to the coils. I am hoping that it does not matter which wire goes to which bolt on the the coil, since it is nearly impossible to tell by looking at the old one which color wire went where (there is no insulation to see the color on the wire). I wired the red one towards the rear of the car and the black towards the front of the car on each coil.

As for the rest, I still need to disconnect the old harness from the starter motor, which should now be significantly easier with the manifold loose. I am thinking that is the last connection to remove, then begin hooking up the "new" harness.

What really concerns me, though, is that I am forgetting where the wires came from, and even worse, where all the vacuum lines run. There have been a million things that I have disconnected, from gas lines, wires, throttle linkages, and vacuum hoses. I hope I can get it all back together properly. What a pain this job has been.
 
#25 · (Edited)
Well what I did when I replaced my engine harness was to remove that support bracket and to remove the ignition coils. I rewired new ignition coils to a new ignition harness, but didn't reinstall them yet. I wrote down where all connections go on the main harness, and just checked everything off as I installed the new harness. The hardest connections to reach were the knock sensor and the crankshaft position sensor. Knock sensor was blocked by the cruise control linkage, but without the ignition coils in place there was room to reach it. Crankshaft position sensor though... Why the hell would you put such an important sensor at the bell housing when you can have it at the harmonic balancer??? I used my magnetic pickup too to unplug it and to align the new harness on it, then I used a long flat screwdriver to push the connector onto the sensor. My hand could just barely fit in there, but it was really painful, due to hose clamps scraping and the cruise control motor and starter motor both being in the way. Everything else was really easy to reconnect. With the ignition coils already wired, it was just a matter of plugging them back in and screwing them back on. You just gotta make sure you wired them right. It doesn't matter where you put the + and - on the coil itself, but it does matter which + you plug into which coil. I also took that time to replace my spark plug wires and my throttle body. Man, what a difference it all made.

But you definetly don't need to remove the intake manifold to do this job. I also suggest you drill a new set of holes on the support bracket and tap them, so you don't have to deal with a nut to remove the throttle body connector, you could even just relocate that somewhere else. The harness doesn't have to go in exactly the same place. I did end up moving some of the grounds around to make it more accessible. By the way, you don't need to remove the large starter motor + wire, there is just a ground wire that screws on to the starter motor's terminals. I reached it with a socket extension and a little mirror from above. Once that bracket is removed everything becomes easier.
 
#26 · (Edited)
Thanks! So, if I am reading correctly, it doesn't matter which wire is on which terminal, but you are saying it is important as to which pair goes to which coil? I searched on the site and saw that another person posted a picture of the wires on the coil that were reversed from how I installed them. If it doesn't matter, I will leave them the way they are, if it does matter, now is the time to fix them!

I just recently replaced plugs, wires, and throttle body, so I am good there.
 
#27 ·
Theoretically speaking, it doesn't matter how you wire the coil up, practically speaking, if it really did matter, than mercedes would probably have paid more attention to the how the wires are plugged in. An ignition coil is really just a fancy word for a transformer. What is actually important is to make sure which the 2 coils are connected to the proper positive terminals. The main harness only supplies the +12 volts from the ECM, the igntion coils are grounded by a very long wire, going to the ground block over the left wheel arch (driver's side). That should be obvious though, the far side ignition coil has a longer wire, the shorter wire wouldn't even get to it.

If you really want to be sure, and if I recall correctly, With the ignition coils installed and their harness plugs facing down, I have the + wire on the terminals closest to the front, with the next one used for ground. I do also suggest replacing that ignition harness, it's only about 20-30$ and it too fails along with the main harness.
 
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