Kenwood KDC-MP538U - no sound.

Car Radio Constant 12V+ Wire: Blue/White
Car Radio Switched 12V+ Wire: Yellow/Red
Car Radio Ground Wire: Black
Car Radio Illumination Wire: Red/Black
Car Radio Dimmer Wire: N/A
Car Radio Power Antenna Trigger Wire: N/A
Car Radio Amplifier Turn On Trigger Wire: N/A
Front Speakers Size: 6 1/2?
Front Speakers Location: Doors
Left Front Speaker Wire (+): Blue/Green
Left Front Speaker Wire (-): Gray/Black
Right Front Speaker Wire (+): Red/Green
Right Front Speaker Wire (-): Brown/Black
Rear Speakers Size: 6 1/2?
Rear Speakers Location: Rear Deck
Left Rear Speaker Wire (+): Blue/Yellow
Left Rear Speaker Wire (-): Gray/White
Right Rear Speaker Wire (+): Red/Yellow
Right Rear Speaker Wire (-): Brown/White

Check the cables in the back of it. If tou already did that how old is it? If relativly new might want to check possibility of wires in back getting wet. If none of those and you have a removable face the connectors between the base and the face are crapping out. Try getting a new face.

make sure you have power going to both the red and yellow wires. also make sure you have a good ground connection.

you can try cleaning the laser lens, or have a professional clean it for you.

Protect indicates that there is a short or a grounding problem usually within the speakers or the speaker wiring. Locate and press the reset button (pinhole). If protect comes back then disconnect all speakers, reset and connect them back one at a time until protect shows up again. This will help you find out where the unwanted DC signal is coming from. If protect shows up when all speakers are disconnected, then it may need service.

some cars have a second wire not with the rest normally yellow it wlii send power tothe player

go to kenwood web site download and print hope this helps

I have had the same problem, my problem was that i accidentaly hooked up the constant wire to the switched, and the switched to the constant, causing it to turn off completely, resetting everything. So if this is the problem then just switch the wires in the back of thew head unit, should be the fatter yellow wire, and the fatter red wire
hope this helps

Check your ground wire

a lot of older cars speakers did not have separate grounds run to each speaker, does yours