Oldsmobile/Buick Repair: 99 Olds Silhouette, fuel level sensor, fuel guage

Question
The first thing we noticed was the overhead display (temp, direction, etc) was reading incorrectly.  Then the automatic door would only open automatically but had to be closed manually (now it won't open automatically at all).  Next I noticed when the headlights were on (at night) some of the lighted areas of the radio and a/c weren't lighting up.  Then the driver's side window wouldn't auto. rollup; sometimes the passenger window won't auto. rollup; now the gas gauge is dancing (never the same way twice).  Oh, and the air pump that's located in the trunk area comes on whenever it wants too but won't work when you want it to. We cannot figure it out.  We have checked the grounding to the battery and the fuses.  Please advise what in the world we can check next.  I really didn't want to take it to the dealer before, but now that so many electrical things are happening, I'm thinking I should.

Answer
Hi
As much as I'd LOVE to tell you just one thing to repair your van, I am afraid you have a bunch of little problems FROM WHAT I CAN TELL.
I looked over all the schematics for all the items you've described, and from experienceThis is what I think....
The DIC (Overhead display) is faulty. They have only an input... thats it. If it is not correct, the DIC module is PROBABALLY at fault.
The sliding doors should be properly diagnosed, but it is PROBABALLY one of the door switches staying opened (electrically open) and not allowing the auto door to function.
The backlighting is preformed by the components themselves...meaning if half the display on the radio is dark, the radio is at fault.
Same for the HVAC controller. They only have 1 wire feeding power for the backlighting.
Windows, again, should be properly diagnosed, but I would guess the DRIVERS side switch MAY be the culprit.
The fuel guage is PROBABALLY the fuel level sensor, located inside the fuel tank. They are a VERY common problem.
The air pump, again properly diagnosed, MAY just be the relay or switch.
I saw no common grounds. As for possible items that could be checked would be to check ALL grounds.
Have the ignition electrical switch checked.
The connector below the drivers seat that passes through for the harness to go under vehicle to rear COULD get water in it, but your year model did not fall under that service bulletin. You MAY have it checked anyways.
I am sorry for the LONG post.
As much as you would hate to do it, you MAY want to take it to either the dealership, OR find a GOOD  auto electrical  repair facility in your area. Ask around.. family, friends, coworkers...
MOST shops (dealer included) MAY charge you a diagnostic fee, that they will waive if you have some or all the work preformed there.
You can set the limit on the fee, meaning say give the shop approval on an hour of diagnostics... That way, you'll only owe them for an hour of work. No hidden charges.
I hope this all helps
Good luck, and follow post back, if needed.
Pawl