take a digital volt meter and check powers and grounds
red ignition switched wire should read with car on and running 12.5 volts to 14.4
yellow constant power comming from battery should read at all time 12.5 to 14.4
black wire is ground and should be ground to the frame of car
lets take your radio ground and put your volt meter black lead on it and then put the red test lead to the read wire and if you have a good ground you get a reading of 12.5 to 14.4 if you car is running if ignition if on accesory it will read 12.5 do the same test to the yellow wire make sure you get a reading without the car on at all . this wire will have power on all the time hint(constant power) or (b+) if no reading on any wires you have a bad ground
let me know what you get for voltage to help you more
to get a good ground you need to scrap the paint off to bare metal and then us a stare washer and use a good stanless steal screw so dont rust for a good ground ..