Has Anyone had 87 300d Wiring Harness Problems w124
 

Has anyone had problems with the electrical system on an 87 300dt?

I have one and the fuse box has all kinds of funky things going on. I measure '0' volts on several fuses (5 or 6) and I'm measuring the before the fuse side of the circuit so it's not a bad fuse.

I've heard things about wiring harnesses going bad. How do I start to diagnose? Where do I begin to look?

The pre ignition harness goes bad on W124s, not the main engine harness.

I'm not familiar with the engine harness (yet), but check the pins on any bulkhead connectors in the system. Then its simply a matter of tracing each wire.

Where are you measuring?
 

Are you measuring on the fuse or on the brass contact?

W124 wiring harness failures are late in the car's production.
You will have wiring problems in a W124 TD, but they will be from bending the harness and will occur at the rear hatch and the doors.....

You can pull up the fuse panel and get to the hard wiring underneath, might be worth having a look see and check for voltage.

Jim

I'm measuring before the fuse (The hot side-Well the side that supposed to be hot). I think I'll be pulling off that pannel and see what's going on underneath. I think there may be some weird things happening though. Because sometimes my instrument cluster pannel illumination works and sometimes not. Also, once in a while my right turn signal blinks fast and sometimes slow. Also, the car dings (The interior dinger/buzzer) while I put it in gear with the door open. Just some weird stuff going on.

A wee bit o "funk" in the wiring. :) Chck for bleed through ( continutity) in wires running together, as the insulation seems to fail.

Do you have the factory tech manual on cd rom? It has all the wiring diagrams and will tell where you should see voltage. The things you are measuring may need the key in the run position or may need to have conditions met to be able to measure any voltage at the fuse. The cd can be a bit pricy but once you use it a few times it becomes priceless (imho) I agree with the fact that the usual places for failure are in the door and lift gate hinge areas.

Ok I just checked a few of the devices that the fuse pannel has no juce on and I think most of them work. This makes it Really confusing now. For example... the Low and High Beam circuit has no voltage at the hot side of the fuse. But... they both work??? What in the world???

Maybe it's the ground....
 

....that you are using when you check for voltage with a meter.

Jim

I don't think so. I used the engine as a ground. Also, if I didn't have a ground I wouldn't be reading voltages on other points in the fuse box. So I think that is ruled out. I do actually get readings on most of the fuses. But there are about 6 or so that have no voltage.

Is there power to the fuse with the lights on?

might I suggest using the neg terminal on the batt for ground, or a bare spot on the chassis. I have found those to be the best.

those fuses seem notorious for getting corroded due to their placement, which will cause them to not conduct even though they may appear in good condition.

when in doubt, replace the fuses. should be step one in troubleshooting an electrical issue on a 124.

in the past i have twisted the fuse in its socket and been able to regain operation of whaatever the fuse was protecting (at least for a little while)

Is there anything wrong with the electricals? Anything specific or just wacky generalized functioning? (Electricals is a word to me BTW....);)

Forget the meter.
I suggest using a small lamp, like a turn signal bulb, as the indicator, it loads the circuit in case there is a high resistance it won't light while a voltmeter will and give a faulty reading. Solder a long set of leads to a small 12V bulb then connect one end to the chassis, the neg terminal on the battery is fine but way across to the other side of the car. I usually find a screw and stick the ground lead under it and anchor it down. Then turn on the ignition and the headlights and touch each of the fuse clips across the hot side of the fuses one by one.
You should get an indication on every one, then go down the other side, the load side and they should also light up the bulb.
You could have a problem under the fuse block where the terminals are daisy-chained together, there are screws under there but I've never heard of them getting loose (there's a first time for everything I suppose)
If your fuses are not the late version that are godlish colored, then replace them all, the whole set is cheap if bought from the right place. The first thing I do when I suspect fuse problems is replace the lot!
If you still have problems give us the fuse #'s