I have a problem that is driving me crazy. I am trying to install a Pioneer CD/Radio in my 91 Escort and can not get it to work. I have the wiring harness and have soldered all the wires. I get power to the back of the new radio but it will not turn on (I have tried two new radios). I unplug the new radio and plug in the old radio and it turns on. Also, the old radio will not work when the key is on ACC if that maters. I know the new radio is grounded so that is not the problem. Any help is greatly appreciated. Thanks.

Why are you soldering wires? The couple of radios that I've installed have all been "unplug the old radio from the vehicle harness... plug in the new". Harness adapters for whatever brand vehicle ... have always been available as the new radio was purchased to make this happen.

The radio has a plug with wires sticking out of it and I bought plugs to plug into the Escort's plugs. I had to solder the wires from the radio to the new plug so I could plug it into the Escort's original plugs.

Had an Alpine. Same thing. Had to ground the chassis of the radio to the chassis of the car. Wouldn't work just grounding the ground wire of the radio.
Had to run a separate ground wire.