more off than on,no heads up display. Defrost comes on. I want to know my speed. on 1992 Cadillac Seville STS

Please DO NOT tell me it's a groundng issue, unless you have specific areas for me to check. I have the wiring diagrams, and have even spliced into the ground wires from the display panel and the passenger side ecu (and ran directly to ground), I've replaced the alternator, reworked the grounding points on both sides of the nose of the car, replaced fuses (and the breakers... yes, breakers), and have wire brushed the power bar in the front power fuse and relay center, but still have the same issue. The display only works on start up, AFTER it has been parked on a slight up hill, and slight tilt to the right. To me, this makes it seem as though it's a power supply issue. It will then go out again once I start driving, or not.

Asked by for the 1992 Cadillac Seville STS