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When I started repairing the rear brakes I noticed a rubber wiring grommet with a cut wire loom from inside of the passenger compartment going underneath the rear right passenger seat and exiting the vehicle on the rear of the car just ahead of the fuel pump... any clue as to what it was? I checked the wiring diagrams and I'm drawing a blank.

Process of elimination, what doesn't work?

Fuel pump
Low fuel light
Fuel gauge
Running lights
Turn signal
Brake light
Fuel door servo
Trunk lid servo
Trunk light

What color codes are the wires?
Are they friction tape wrapped?

BMW wiring color codes are impeccably accurate and easy to trace with a Haynes manual.

Yellow/green; brown; blue thick wires in what seems to be a black factory plastic protective sheath.

If something doesn't work because of it missing then I am unaware of what it is. Fuel pump works. Gas filler door seems manual. The windows are manual.

lazytv wrote:Yellow/green; brown; blue thick wires in what seems to be a black factory plastic protective sheath.

If something doesn't work because of it missing then I am unaware of what it is. Fuel pump works. Gas filler door seems manual. The windows are manual.

I was looking at my wiring diagram for other things and looked that up. Those colours might be tail light wiring. Does it/did it have a tow bar? Someone may have cut it up and re-routed the wiring for a trailer plug. Is your light wiring factory?
Just a guess..

post a picture with some perspective to it.

You can see the rubber boot protruding out of the bottom below the seat of the rear passenger.
<img src="https://lh3.googleusercontent.com/-0km0 ... 140230.jpg" height="300" width="400">

And here you can see that I've pulled the wires out of the boot and stripped them back to reveal the colors.
<img src="https://lh3.googleusercontent.com/-G1Pd ... 140105.jpg" height="400" width="300">

Fuel pump wiring loom. If you look at the Fuel pump itself and fuse box and/or positive battery terminal, you'll probably see a non original wire added, which is someone's idea of fix for a flakey original fuel pump connection.

My pump works.. fuel gauge doesn't.

Fuel pump is only 2 wires, gauge sending unit is three wires so likely your gauge harness.


Ralph

lazytv wrote:My pump works.. fuel gauge doesn't.

Well, there you have it. You never answered the question "What doesn't work" so I couldn't help you. In my car, the only harness entering the boot as you describe is the fuel pump harness. The fuel gauge sender harness is part of the rear body harness, along with the tail lights, etc. I guess they must have re-routed things in later cars, since mine is pretty early. So now you know!

The wiring that comes through under the rear seat is for the brake pad sensor on the right rear wheel. Fuel pump wiring passes through the rear bulkhead and through a plug in the floor of the trunk.

Fuel sending unit wiring is part of the main car harness and breaks off below the right tail lamp, runs up the trunk floor then under the access cover where it plugs into the fuel sending unit.