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Make your own wiring loom - Here's how I did mine...

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47K views 64 replies 32 participants last post by  Sweafox  
#1 · (Edited)
Well, it was bound to happen... It's a '92 500SE with almost a quarter million miles on the clock, so the original loom did pretty well!

All was well untill I took the car off the road for a month to fit the hydraulics (story to follow in a few weeks). I must have disturbed something, as the car would start-up and run OK until warm, then one bank would shut down. Not good. I figured it was the loom (as most people on here seem to have come across this common problem at one time or another), so took some covers off, and indeed, things were not looking good:

Image


I enquired at the stealership for a new one - £532, which is just over $1000 US. Bugger that, I'll make my own...

Wire: £15
Heat shrink: £3
Electrical tape: £1
Tweezers: £1

Total cost: £20 (oh, and two evenings work!)

So, out with the old:
Image


When I started to strip it down, I realized just how bad the original loom was - how was this working at all?!
Image


Image


Trying to figure out how to get all the connectors apart without breaking them was the biggest challenge, and the main connector to the body was the most awkward. It took an hour of very carefull prying to get all the glue/waterproofing out before I could pull the wires through enough to expose both sides of the connector.

Then there was the problem of getting each pin out. By pushing into the little slot each side of each pin with a modified (ground down) pair of tweezers, I could release each pin in turn:
Image


Same method was used for the injector connectors:
Image


Image
 
#2 · (Edited)
I carefully cut all the knackered wire from each connector, then soldered in new wire. Here are two injector pins with new wire:
Image


And back together:
Image


What better place to repair the loom than on a Mercedes v12 coffee table in my front room. Luckily, I have a very cool/understanding wife!
Image


A couple of the connectors required some head scratching on how to get them appart. This 4-pin connector at the front on the engine was one of the more interesting ones!

Carefully cut around with the Dremmel:
Image


New Wires soldered and in place:
Image


And melted back together with the soldering iron:
Image


Yeah, I know, not the neatest job, but it is strong, water tight and you really don't notice it back on the car.

OK, the MAF sensor... With thanks to one of v12Uberalles excellent "how-to's", I knew how to get this connector appart - unfortunately, I'm an impatient kind of chap, so cut it open with the dremmel!
Image


It actually cleaned up nicely when put back together - honest!
 
#60 ·
Post 2...

ScrapingScrap said:
I carefully cut all the knackered wire from each connector, then soldered in new wire. Here are two injector pins with new wire:
Image


And back together:
Image


What better place to repair the loom than on a Mercedes v12 coffee table in my front room. Luckily, I have a very cool/understanding wife!
Image


A couple of the connectors required some head scratching on how to get them appart. This 4-pin connector at the front on the engine was one of the more interesting ones!

Carefully cut around with the Dremmel:
Image


New Wires soldered and in place:
Image


And melted back together with the soldering iron:
Image


Yeah, I know, not the neatest job, but it is strong, water tight and you really don't notice it back on the car.

OK, the MAF sensor... With thanks to one of v12Uberalles excellent "how-to's", I knew how to get this connector appart - unfortunately, I'm an impatient kind of chap, so cut it open with the dremmel!
Image


It actually cleaned up nicely when put back together - honest!
Click to expand...
 
#3 · (Edited)
Loom now complete except main connector:
Image


Just this little bunch to go:
Image


Now I know I used all black wires, which may cause issues if I ever need to trace a fault, but I figured that there are only 22 wires to the main connector which would never take too long to trace, and one roll of black wire costs way less than 22 rolls of multi-coloured wire!

Main connector coming back together:
Image


Completed loom!:
Image


And back on the car, it's all looking fairly good:
Image


Only made one small error - the wires to the front-of-engine connectors were very slightly too short (note to self: measure twice, cut once!), and would have been a little tight through the original ducting, so they now come out a couple of inches further up, but it still looks neat enough:
Image


Pic of main connector installed with new cables:
Image


On starting it up, I couldn't believe the difference! The engine has always wobbled slightly when idling - now it just stays completely solid. It seems to want to rev more more freely, and there is definately more power (especially low down torque). And even after sitting in traffic for a half hour, it just purrs contently! I guess the old loom had been on it's way out for a long time...
 
#61 ·
Post 3...

ScrapingScrap said:
Loom now complete except main connector:
Image


Just this little bunch to go:
Image


Now I know I used all black wires, which may cause issues if I ever need to trace a fault, but I figured that there are only 22 wires to the main connector which would never take too long to trace, and one roll of black wire costs way less than 22 rolls of multi-coloured wire!

Main connector coming back together:
Image


Completed loom!:
Image


And back on the car, it's all looking fairly good:
Image


Only made one small error - the wires to the front-of-engine connectors were very slightly too short (note to self: measure twice, cut once!), and would have been a little tight through the original ducting, so they now come out a couple of inches further up, but it still looks neat enough:
Image


Pic of main connector installed with new cables:
Image


On starting it up, I couldn't believe the difference! The engine has always wobbled slightly when idling - now it just stays completely solid. It seems to want to rev more more freely, and there is definately more power (especially low down torque). And even after sitting in traffic for a half hour, it just purrs contently! I guess the old loom had been on it's way out for a long time...
Click to expand...
 
H
#5 ·
I like the Guiness on the table haha
 
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#9 ·
Awesome work! Thanks for sharing.

Question: Is that a V12 engine block holding up your coffee table? Way cool! :thumbsup:
 
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#15 ·
Outstanding innovation and inspiration to all.
Robert is in his corner applauding and yelling "WAY TO GO!"at top of his lungs. Fantastic to see this quality of work.

As suggestion... support your multiple conductor/pin in connectors at the area just before (50mm or so) each connector with tape or shrink sleeve as in "MB factory production harnesses". Reason: The harmonic vibration of the engine can/will cause premature failure at conductor to pin solder connection(s). Reared evidence in Failure analysis of vibration of "multiple soldered conductors" with and without circular support 50mm to 70mm of connector pin solder of multiple conductors.

Great to witness this type of work! Dietrich
 
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#27 ·
Nice job ScrapingScrap. I wondered if other people rebuild those themselves.
I wanted to see pictures as well but they are no longer show. I rebuild those harnesses as side income and would like to see other people do it. My pictures you can find on my website Mercedes repair and restoration under "Main engine wiring harness rebuild" tab to the left. Not a spam here :) I had 1992 S500 and my harness was shorting everywhere. Car used to stall on intersections and hitting bumps. It was horrible. I refused to pay "stealer" $750 for new harness so I rebuilt mine. It took about 8 long hours to get it right. I love Mercedes cars and decided to start offering my rebuild services as side job.
If anyone would needs to rebuild their harness, contact me from my site. It's hard to keep tracking posts.
Thanks
 
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