I have a 98 Bonneville SE with Bose equipped stock system. I recently hooked up an aftermarket head unit using a wiring harness and everything works fine, sound and all, the only problem is that even when the car is off the head unit remains powered. This led to the previous battery being killed when the car was off. I have the wiring hooked up properly as far as the color coding goes, and the yellow power wire is hooked up to the corresponding yellow wire on the harness, so it should be receiving switched power, not constant. In case this matters, since it'* Bose equipped it has a lone orange wire for powering the amp which I have connected to the yellow power wiring as that is the only way to get sound to play through the speakers. I don't know why the head unit is constantly powered so my temporary solution has been to disconnect the harness while the car is not in use but that is pretty annoying. Any ideas?

I have the fsms and confirmed yellow is accessory aka switched and orange is battery.

Check the colors where your harness goes to the factory harness and make sure the wires are in the right places where your harness connects to the factory wiring. I've seen a couple aftermarket harness connectors with incorrect placement.

if you keep having that problem, run an accessory wire to the ignition, which is normally a pink wire. but that will make it so when the car turns on, the deck turns on/off