91 Dodge Ram radio ills

I thought my radio was toast,so I bought another which worked perfectly in the car it came out of.

MY old radio just lost power,no clock,no power anwhere. New good radio,same thing.

now the kicker. A test light says the power is fine coming in to the radio. Both sides,one constant for clock,one switched for radio.

So I imagine a 'grounding issue?' The first two wires closest to steering wheel were power wires,,,which one would be the ground wire?

AND the new radio in the wrecker car didnt even need the ground strap on back to be connected to work,,,The ground strap on my setup goes to a metal mounting bracket underneath dash.

Oh by the way,most mysterious problem was with old radio,last time it played (years ago)you turn the radio switch off and it stayed playing,till you turned truck off,,,nothing made it stop!!

So where do I look now?? Can YOU help me excorcise my radio demons??