Sometimes the unit will reset itself if you pull the fuse out for a minute then reinstall the fuse.
Couldn't tell you why, but I can tell you how to fix it. Unplug the negative terminal on the battery (make sure the car is off) and let it sit for 5-10 minutes before re-plugging it. This will reset the radio and eject any CD that is in the CD player.
I'd recommend http://www.DelcoLockCodes.com. They can get the code for any locked Delco radio. Good luck!
http://www.installdr.com/Harnesses/GM-Wiring.pdf or try haynes.com
Yes they should be interchangeable
The 'P" button searches the next programmed station that the radio is set
Delco is the electronics arm of GM. They have produced things like radios and other electronics for GM cars and trucks over the years.
Yes, though as of today NY times stated GM may sell or merge ac delco with chrysler.
Pretty sure that's fits eighties Chevy citation. Was a kinda weird vertical design.
GM
Yes
Any GM dealer.
It's an AC Delco Knock Sensor Module