1988 Cadillac Sedan Deville
http://www.installdr.com/Harnesses/GM-Wiring.pdf

I installed a new head unit, but in the wiring harness I had, the power connecter was the 2 wire version while my car has the 3 wire version. I had to cut off some plastic to make it fit, and ended up plugging it in upside down accidentally (so the yellow wire labeled "12 Volt Battery/Constant" on the wiring harness was connected to the car's orange/black-striped wire, instead of the solid orange wire). When I tried it out, it worked fine until the bass in the song came in, at which point the dashboard display (speedometer, fuel meter, AC/heat) started dimming and then cut off (the head unit cut off too), followed by a burning smell. After I flipped the power connector, the head unit worked fine again, but the dashboard display still didn't work. I checked all the fuses visually and with a continuity tester (the main fuse box and the other ones under the dash on the passenger side), but didn't find any bad ones.

What did I break?

I Had Virtually The Same Thing Happen To My '88 Coupe Deville. Determined I Had Shorted The Bcm (body Control Module) Got One At A Pick And Pull Wrecking Yard From An '87. Swapped It Out And All Was Ok. Unit Is Located Behind The Glove Box, Necc To Remove The Glove Box Liner To Gain Access. If I Remember Its Held In With #10 Metric Bolts. If You're Not Sure What To Look For, Its A Silver Metal Box Smaller Than The Ecm. Good Luck,, Bill.

After reading your response, I went to a place called U-Wrench-It and pulled a BCM from a 87 Deville (got a headliner in excellent condition from the exact same car a few days ago :)). Just put it in my Deville, and everything seems to be working again :bouncy:. Thank you.