need help on wiring harness question 94 e320 - PeachParts Mercedes-Benz Forum

fulltimefamily · #1 02-22-2006, 02:56 PM

Thanks for taking a look at this.
I suspect that these wires (shown in photos attached) are not part of the wiring harness being replaced in the DIY article.

I hope this shows the location in the three photos attached.

This assembly seems to have one white/purple and two smaller brown wires. The insulations is badly deteriorated on all three.
They proceed from the firewall joining with a heavier wire (which also comes out of the firewall in the same location) into a protective sleeve near the oil filter housing and continue down where the heavy wire attaches to the starter solenoid. I can't see where these three damaged wires branch back out and attach.

By the way, I took it to my mechanic because my mileage had dropped from 25mpg to 19mpg and my check engine light was lit for two weeks before going out on its own.

He checked my codes
Resulting in: 42-injection valve cylinder 2 short to battery voltage.

No codes or check engine light after resets and test driving
No lean or rich fuel indications by test equipment.

My Question is: What wires am I looking at and can a DIYer replace them?
Could they be the culprit in poor gas mileage?

Although, I realize that the main harness is probably bad too, I wondered if these wires should be replaced first and perhaps cure my current woes.

Any thoughts welcome and thanks for all the information I've gleaned by lurking and reading over the past few months.Attachment 31750 Attachment 31751 Attachment 31752

Kestas · #2 02-22-2006, 09:29 PM

Keep in mind some mechanics won't even attempt to diagnose driveability problems on your model until the engine wiring harness is replaced. The wiring harness can easily be the cause of the problems you're experiencing. Even if it doesn't solve your immediate problem, the money won't be wasted.... it'll preclude niggling and perhaps serious problems in the future.

It's not a difficult DIY job. If you don't rush, it should take you 2-4 hours to replace the engine wiring harness. Just lay out the new part over the old under the hood and start swapping connectors. The part will cost roughly $800-900.

Please replace it.

kidMoBile · #3 02-23-2006, 07:43 AM

Absolutely right. If your wiring harness is original, the insulation on the wires probably looks just like the wire you're looking at or worse. To see if the harness is original, there's a white part number tag on the harness right by the battery which has the date of manufacture for the harness. You may have to move the battery slightly to see this tag....if I recall correctly the harness runs just behind the battery and the tag is in that vicinity. The main harness is the one that feeds from the computer behind the battery, then from the battery compartment through the top of the front firewall and into engine bay at the rear of the engine. It then runs along the top of the motor, front to back, underneath a long black plastic trim piece that is bolted to the top of the engine. Take a look at wires near the top of the thermostat and check condition (Don't wiggle them! Just a visual check.) The insulation on a bad harness will be cracked and/or falling off. But if you don't see decay, that doesn't mean the harness still isn't bad. There were 3 different harnesses for the 93-95 M104; give your VIN# when ordering the part.
The original harness was made with wires that have thermally unstable insulation. THEY WILL ALL FAIL with time and heat on these cars. It's just a matter of time before it starts causing a problem. My car had 55K miles and was 8 yrs old when I did the harness. The car was getting 14mpg and exhaust smelled horrible, but no fault codes were recorded in the computer. Changed the harness (4 hrs, but I'm slow!) and all was good. I get 18-25mpg now as I should.
Letting a harness get to the point where it is really screwing things up could damage peripheral systems, IMO. You've got renegade electical signals crossing from one wire to the next, etc.
My harness was the most expensive of the three...today's price is slightly over $1000. I got mine from Phil here on this site at Fastlane.
Do a search on "wiring harness" and grab a beer......you'll be reading for a while. I posted a replacement procedure, and there's a nice procedure written up in the Do-it-yourself section of this site.
Good luck!
Brian

fulltimefamily · #4 02-23-2006, 10:16 AM

Thanks for the advice and I will do the main wiring harness asap.
However I still wonder if there is more wiring I need to get to.
I suspect the wire harness in my photos is coming from the ingnition switch and is not part of the engine wiring harness. My question still remains as to what part # or name to request and is this a section of wiring replacement that can be attempted by the average DIYer.

Again many thanks on the main harness question (i have searched and read the forum on this). Any advice now on this smaller wire section appreciated.

Thanks again,
Ray

lkchris · #5 02-23-2006, 10:47 AM

A brown wire in a German car (or motorcycle or truck) is a ground.

Kestas · #6 02-23-2006, 11:19 AM

Ray, I believe you're wondering if those wires are part of the engine wiring harness assembly you've researched so thoroughly. It's hard for me to tell by the pictures, but if you follow the wiring from the main bulkhead behind the battery, see if any of the wires branch out to the wires you presented. If not, then the problem needs to be dealt with separately from replacing the engine wiring harness.

The wiring in the whole car is made from this brittle insulation. It's the heat from under the hood that accelerates damage to the engine wiring harness, and makes this problem mainly confined to the engine wiring harness.

e320_Coupe · #7 02-23-2006, 12:55 PM

Those wires are not part of the engine wiring loom. I replaced mine by opening the connector and soldering new wires in (there's only 3 IIRC). I suspect it's cheap enough to buy the small loom from a dealer if you don't feel up to it.
You may find that the main engine loom has already been replaced which is why you don't have any error codes. Check before committing to replace the entire loom.

PaulSpringmann · #8 02-23-2006, 01:40 PM

I replaced this on my '95 E320 Wagon as I had the same problem; it's pretty straight forward and is not part of the main engine wiring harness. Tell the parts guy to look for the positive battery cable harness as this is the main large wire and how it is listed in the EPC. One end is snaked to thru firewalls to the battery. Near the oil filter on the false firewall, there is a plug connection. It ends up at the starter and one of the wires is connected to the oil level sensor on the starter side of the engine. If you can't find the part number, I'll try to find it in my receipts when I get home. I think this part cost $60 4 years ago.