June 5

1994 Mercedes S500, Engine Wiring Harness Replacement



Mark: Hi it’s Mark, Top Local, we’re here with Bernie Pawlik, Pawlik Automotive in Vancouver, we’re talking cars. How’re you doing Bernie?

Bernie: I’m doing very well.

Mark: So we’re going to talk about a Mercedes S500 wiring harness replacement, what was going on with this car?

Bernie: well this car was brought to us by a client of ours for a couple years and he had an intermittent issue. The car sits in a garage for a long time, takes it out for a drive, maybe for 15-20 minutes, stops the car, gets back in, drives it, runs really rough for a while. It had been serviced at the dealer, it’s a very low mileage car, previously I think, just exclusively serviced at the dealer. They replaced some distributor caps, a few things but still the problem persisted and what we figured that was likely based on the symptoms, that there was a wiring harness problem which is a fairly common issue to these vehicles.

Mark: So a wiring harness replacement sounds like it could be pretty expensive?

Bernie: It is actually extremely expensive, not really as labour intensive as you might think on this vehicle because of the age of the vehicle, but the part itself is extremely expensive, but what happens with this wiring is it actually disintegrates. It’s a defect that Mercedes has had from about 91 to 96 model years, sometimes extending into 97 from what I read and basically the wiring just, the insulation they use, some kind of insulation that basically flakes apart. There’s really nothing you can do about it. I’ll share a couple of photos.

1994 Mercedes S500, Engine Wiring Harness Replacement
1994 Mercedes S500, Engine Wiring Harness Replacement
1994 Mercedes S500, Engine Wiring Harness Replacement
1994 Mercedes S500, Engine Wiring Harness Replacement

Here’s our 94 S500, a real nice, real nice condition, a four door sedan, lots of leg room front and back, very luxurious features for a car of this age. So this is the complete engine wiring harness, this is the old one that removed from the vehicle. Basically this harness goes from the fuel injection computer goes to all the various sensors and also the fuel injector so that’s kind of primarily what it controls. This vehicle being of the 94 vintage, it also has an ignition computer which is a separate thing, doesn’t seem to be any issues with the wiring on that particular side of it, but it’s with this particular wiring harness. Now let’s have a look at some of the wiring. So this, if you can see here, this is the wiring connector to one of the fuel injectors, maybe you can see this insulation is just basically broken right off the wire and another view here, this is with the plastic cover stripped away, you can see the insulation is just cracking, cracking, cracking all the way up. This is happening on every one of these wiring connectors. So basically what we figured was happening with this vehicle, and we don’t know for certain, is that you know, sometimes when you run the vehicle a wire would short out or something, a bad connection would occur and that would cause the engine to run roughly. Incidentally, it never happened when I drove the vehicle and I drove it quite a few times but this is the kind of nature of intermittent problems. Now again, it’s one of these things where we replaced it because there’s no other obvious fault and the wiring is such an obvious issue that it makes sense to do it. The other thing that can happen with these, with this particular issue is that these wires short out, it can cause failures of other components, like it could actually blow the ECU, you know extremely expensive. So if you’re going to keep the car and you want to do it, you got to fix the wiring first.

Mark: So I think you mentioned this, but this was was a certain range of years, all different models of Mercedes in those years?

Bernie: Yeah all models of Mercedes from 91 to 96 and I was reading somewhere into 97, so anything around those kind of model years is when that insulation happened, is bad. Yeah it affects all models anything from a four cylinder C series up to the S, any AMG’s anything, it affects them all.

Mark: So would it have been maybe more cost effective to just have insulated those wires?

Bernie: Well there’s a lot of them and they all deteriorate so unfortunately not. I mean, I guess if you really wanted to go cheap and you’re really handy, you could probably take the wiring harness apart and replace each individual wire but you know with all the connectors on there and the precision that’s involved in all these components, it just makes more sense to replace the complete harness. It’s not a cheap part, only available from Mercedes or there are people who actually custom rebuild them but the price, the price is less but I don’t know, I just trust the OEM harness a lot better and the new ones have been redesigned not to rot which is an important thing.

Mark: So this is a 94, getting pretty old, was it worth doing this repair?

Bernie: Well that’s a good question and it really depends on the car, I mean for the owner of this vehicle there was some sentimental value, the car is very low mileage, only 57,000 kilometres, essentially it’s like a brand new car still, so really well maintained. So if you you care about the car, it’s a nice, Mercedes are nice quality vehicles in any model line, it’s really how much do you care about the car. There’s certainly some models like the AMG or an S or SL series, they’re still worthwhile, and some are collectible so you know, they’re definitely worth the money. You just got to sort of assess it yourself. For a C series car, four door sedan probably not but you know, for a nice one yeah, it’d be worth it.

Mark: I’ve actually ridden in one of these, these are a very, very nice car.

Bernie: It’s a super nice car. It’s got some amazing features like little blinds that go up on the back window so you don’t sun shine in and the leg room in the back again, you could take four large men and put them in this car and they’d be extremely comfortable driving right across the country. So you know there’s something to that, even the back seats recline and they’re amazing features for a 1994 car.

Mark: So there you go, if your 94 or early 90’s vintage Mercedes is showing some issues, you want yo call Pawlik Automotive, they can look after you. You can reach them at 604-327-7113 or check out their website pawlikautomotive.com. Thanks Bernie

Bernie: Thanks Mark

About the author 

Bernie Pawlik

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