There is a DIY article here on how to replace the wiring harness. It has step by step instructions and pictures. I can't recall for which engine it was. It seems like a fairly straight-forward thing to do, not any more difficult than changing plug wires.
My daughter's 300TE had some stalling issues. Enrique at Mr. M.B. MOTORS diagnosed the problem as a wiring harness issue. Before ordering a new wiring harness, Enrique took the time to check the wiring and was able to locate the culprit. Some wires were cahnged/re-routed and now the car runs great. We did not need to change the entire harness.
I know we all wish that MB would fix all of our cars' problems. But I have to tell you, I have owned many different brands of cars, it is hard to find a car built as solidly as the W124 or the W126 bodies (I have no experience with newer Benzes). My daughter's 300TE has 190k on the clock and it runs like a champ. Several years ago I sold my '84 300SD with over 300k on the clock, that car is still running strong. The new owners (family friends) still drive it on a daily basis and they love it. BTW, the husband is a German engineer and he loves diesels. I sold my '91 420SEL with almost 250K on the clock. That car is still running great. The new owner took care of the few problems that it had and she loves her "new" car.
By contrast, I now drive a 1999 Seville SLS. Talk about a POS. It has 48k miles and it has been in the family since it was new (it was Dad's car). Since October of last year it has had over $6k worth of tranny work. Fortunately for me, I bought an extended warranty, so all the repair bills have been paid for by GM. I, however, shudder to think what will happen when the extended warranty expires.
If you think that MB is cold and heartless towards its customers then try dealing with GM. The GM "customer care" center is the biggest joke in the world. For example, my highly touted Northstar engine, allegedly the best/greatest/finest engine ever made by GM (at least according to their own literature) consumes one quart of oil every 750 - 1k miles. It has been doing this since new.
When Northstars owners complain about the engine's thirst for oil, GM's reply is: 1. this is normal, 2. manufacturing tolerances (or lack thereof) cause some engines to consume more oil than other engines, 3. this is a "built-in" feature to make sure that there is always a supply of fresh oil in the engine or 4. we NEVER heard of this problem (I actually got that answer once).
Sure, it would be nice if Benz fixed the wiring harness problem, or if they took care of the cracking dashboards on some W123 or W126 cars or if they fixed the peeling clearcoats on some older Benzes. But try finding another car that will consistently give owners such driving pleasure and longevity of use and I am sure that you will find that no other car comes even close to Benz.
So enjoy what you have and thank God that you don't drive a Cadillac Seville. (BTW go to
www.cadillacforums.com and see how even the much-touted new STS is full of problems. GM will NEVER get it right).
Enjoy.