Grounding issues I think....

I'm new to the forum and have found some useful info on probs I've had looking through all the threads already. But I'm haveing one problem I can't figure out I'm waiting on a book on my car right now sense the last fix cleaned me out for extar spending cash right now. I was wondering if anyone had a wireing diagram for a '90 Grand Prix LE 3.1L for the dash. I have a bad ground which seems to be comeing from the ground right above the diagnostic connect on the right of the steering wheel. I've notcied it more sense I've installed a sub for my stereo (I've trying caps or condencors at the altenator) Its not ingnition noise from what I think sense it doesn't rise or lower with rpm's. has anyone had this problem before??? Its mainly like feedback (if I turn my amp to loud all I get its a continuous hit of bass outta the sub). I've been trying to trace the wire with no luck sense just about anything (gauges, light and wipers switches, etc.) give continuity senses its a ground :banghead: . Does anyone have any ideas cuz I really don' want to have to tear the dash out and rewire every ground in there... its half out as it is but I need the car back on the road for monday.

Matt

Actully I have a update on that last post I just jumped for codes I get code 43 for the ESC the possible causes are
Possible causes:
Open or shorted knock sensor
Loose knock sensor
Excessive mechanical noise within engine
Improper or incorrectly installed MEM-CAL in the ECM or defective ECM
Intermittent open in the EST line to the ignition module

Also it says about a loss of ground at the ESC (electronic spark contorl) Does anyone know where this ground wrie is exactly??? I know its under the coil pack if I'm not mistaken but I can't really see and ground wire coming off it. I'm going back to check now any help would be apperciatied on this

Matt