1990 Econoline

Hi,
I have just bought a 1990 e150 limited edition (coors light silver bullet??)

The van is in great condition, runs well and has only 80,000 miles.
BUT! it suffers from a miriad of electrical problems.

I guess who ever did the Coors Light Conversion, did there own wiring, and has added to the factory harnesses. The problem i have now is that i can not figure out what is factory and what is a secondary conversion addition...

None of the gauge lights work.
the rear lights dod not work, although the brake lights do and the rear turn signals do. the others do not.

I put in a new light switch, the pull and turn type.
When i pull it out the front lights come on only. when i turn it one interior light comes on and then won't go off until i disconect the battery.

When i switch the lights of (ie push the switch in) the lights stay on for about 2 mins then go off??

All fuses are ok, but the wiring harness has so many, what look like professional additions, it tough to figure out what goes where and how.

The fuel gauge only works when i switch to the rear tank, does this seem like it's conectted to the other electrical faults or is it likely that the front sender unit is hosed or has a bad connection somewhere.

Any help at all would be great, i just know if i take it to an electrical specialist, i can kiss a $1000 or more good by.
Thanks for any help.
cjspga