[320sAndrew]

First off the car is a 1995 S320. I recently put new Bosch plugs (gap has been checked and re-checked) and the car started running badly with a very rough idle and no power. My next logicle step was to change the spark plug wires. About $160 later I completed the swap. The car ran even worse after I replaced the wires. I then made sure the firing order was right even though I changed only one wire at a time. I left the car running and checked the wires again, I noticed some exposed small gauge wiring running into the coil packs. I exposed more of those wires (I assume they are just the low voltage wires running to the coil packs) with the car running I wiggled these small wires around a bit and found it affected idle quite a bit. After further inspection I found that the two wires inside the looms running to the coil packs were not insulated and contacting each other. I guy I talked to at Performance Imports who I deal with alot in ordering parts and asking questions said he ran into the same problem and was told the wire insulators were biodegradable and made of soy bean. He wanted $500 for a new harness from the plugs to the fuse box. My question is could I use high temperature wiring and replace the uninsulated parts of the harness and basically create a partial wire harness? As of now the car will not turn over.

 

[deanyel]

You must have one of the last cars driving around on an original harness. The harness fails first closest to heat but the entire harness is suspect. Whereever you decide to tap in you'll be messing with the upstream wires and potentially causing damage there as well. I wouldn't say a partial fix is impossible but it's not likely to be long lived or reliable. Some have rebuilt the entire harness but it's a fairly labor intensive exercise. BTW, $500 is a good price, list is about $635.

 

[320sAndrew]

Thanks for the suggestions. The car did sit a long time. My parts guy is good and honest. Needless to say I have put a lot of money into this car to keep it on the road. Any other suggestions or comments would be appreciated.

 

[320sAndrew]

I tapped into my wiring harness and rewired the section I found to be in the worst shape. All went well and I was very careful to be exact and do a clean job. Unfortunately it didn't work. Upon further inspection the old harness is junk. How hard would it be for a somewhat experienced mechanic to change the whole harness? It looks simple but I was always a Volkswagen/Audi guy before I bought this car and where I work the most I've done to a Mercedes is oil changes, brakes and tires. These cars are so enjoyable until something goes wrong so I'd hate to give up the old beast.

 

[deanyel]

Depends on what you mean by change the whole harness - install a new one or build one from scratch. Installing a new harness is not that hard, just have to stay organized. Dealers have been known to charge six hours of labor but a good mechanic can do it in less than an hour and half. I did it as a first timer in 3 hours, moving very slowly with great care.