W126 Messed-up fuel pump wiring? Bad pump?

[DRothmann]

Hi All,

As a brand new DIY Mercedes owner I have searched the net for weeks, looking for MB sites to add to my favorites. This seems to be the best, most knowledgeable and most lively place at all. Huge amount of info and great discussions.

I am still an amateur, but have done a lot of work on my previous BMW 7 series (E23) and on my Audi 100 1989.

The Story:
My biggest challenges has always been previous owners messing with the wiring and my newly accuired Mercedes also falls into this category

At some point of time someone had an Alarm/Start inhibitor installed, then it stopped working (or something), so this was rewired/shorted.

Now I just realized that the custom switch installed on the lower dash (to the right of the brake release lever), which I believed was for a previous installed extra headlights or something - is actually turning on/off the fuel pump, I can hear it hissing when I flip the switch - even with the engine stopped

The request:
So I need to check the entire wiring to my fuel pump (or does it have two?) - as I have not found a wiring diagram yet, I really need some help here.

A wild guess:
My old BMW's had two fuel pumps, if one died it would still run but the remaining pump would get worn out fast and start giving drivability problems. If the fuel pump (as mentioned above) is only running when I flick the switch - would the car still run? - If, then could the other pump end up giving symptoms like this (which started after driving 2000Km without any problems):
- car runs fine, with a little problems accepting full throttle
- then after about half an hour of driving it will only take very little throttle otherwise it feels like massive misfiring or maybe fuel starvation?
- stop engine for 5 minutes and it will run fine again for 15-20 minutes until something gets hot again (fuel pump).
(I have replaced rotor, cap, wires and plugs and tried another ignition module).

Thanks.

[mbdoc]

If you have an e-mail address that you can send to my e-mail? I will send you that wiring diagram. The file is way too large to post here.