Trunk Wiring problems of the 1999 Oldsmobile Intrigue

This car is an electrical nightmare. The Intrigue seems to have so many of the same alero problems, but no resolution from gm regarding them. Vehicle continually will: not start, start and then die, have the instrument cluster go haywire (all gauges drop to the bottom, then jump back up, lights coming on then going off - abs, check engine, service engine, etc) additionally - security (passlock) light will come on sometimes when the instrument cluster goes nuts, and then will stay on. This often leads to a no-start condition. If battery is disconnected for a few minutes, this will usually resolve the issue. Sometimes, when there's a no-start (no cranking) - turning the car to acc, and then moving the shifter through a couple gears, will resolve the issue. When there's a no-start (with cranking) - this can eventually be resolved by disconnecting the battery for a long time. The gauges going crazy while driving: often, when not actively pressing the accelerator, the gauges will drop to the bottom (empty gas tank light comes on, rpm, gas, and heat needles drop to zero; speed usually remains functional). When pressing the accelerator, they all pop back up to functional (only to drop again when there's no acceleration). The key - can be taken out of the ignition switch while the car is running, with no resistance. I have replaced: battery multiple times, battery cables once, the ignition switch & cylinder have been replaced at least once or twice by a mechanic trying to resolve the issue; wiring harnesses within the engine compartment and below the steering wheel have been replaced.