Wiring Harness Inspection (W124- 1994)? Procedure?
 

FYI- Wiring Harness Question Again....

Does the exterior protective sheathing have to be opened to properly inspect for interior insulation cracking/failure?

...the '94 E320 Coupe is coming off of Starmark this month and Factory Auth Service here in San Francisco will be inspecting the wiring harness this Friday

tks-fad

yes, IMHO, because there are no external signs as everything is wrapped in the black sheathing...

Defective Wire insulation
 

By all means , carefully slit open all the wiring harnesses that are exposed to engine heat and check the condition of the wires inside.

You should make the slit with a straight edge razor blade or aircraft hijacking weapon (excuse me box cutter), preferable on the side most exposed to the heat. A 2" long slit is plenty. pull some of the wires out of the slit to see if they are still flexible and sound.

i checked my old harness, it seemed ok in spots but saw places where the wire was bare. check the connectors, that's where insulation can just fall off and short...

I just recently went through this. I had the harness inspected at every service visit. It wasn't until I pulled the plastic engine cover and air box off and looked myself was it noted. I could see it plainly on the wires as they came out of the sheathing to go to the connectors on the temp sensors at the front of the engine and onto the fuel injectors.

Now, here's the kicker. I had the "wiring harness" replaced, then the check engine light came on. It went back into the dealer, and that's when they found that the lower harness was also bad. I didn't until then know that there was more than 1. It turns out that the lower one is MUCH more expensive and more time to replace. To the dealer's credit, they did it all, and didn't charge me a thing. (They billed 14 hours! of warranty labor on the invoice for the lower harness!!!!).

Moral of the story, ask them to inspect both upper and lower harnesses, carefully, then do it yourself.

For a non-intrusive test of the engine harness, the plastic cover can be removed as previously mentioned and inspected where the wire comes out of the conduit and runs to the 2 switch-over valves (AIR pump divert valve and EGR valve) and to the cam adjuster solenoid (often confused as a cam sensor, which it doesn't have), and also the ground wire at the front engine lifting eye, and the temp sensors as noted.
I am unfamiliar with and have not needed to replace anything but the engine harness, the lower harness as noted may actually be a harness that runs to the inside of the instrument panel, which would really be a big job to replace.
The usual problems when the engine harness starts to fail is either incorrect or no operation of the EGR or AIR injection system (logic function chain codes), or possibly inop fuel injectors on real bad ones. I've heard slicing open the harness to the MAF sensor is also a good idea if the harness is suspect due to cracking wires in the switch-over valve area.
Gilly

A hearty thank you for your time and advice guys!

-fad