Originally Posted by Chris_1997_XJ
... putting the front powers windows up using the switch will cause the radio's power and sound to fade?
Wiring issues in the XJ front doors are common. If you have a short circuit in the door wire harness you can have a loss of connectivity or you can have 12 volts feeding directly into the speaker wires. Most head units have a circuit breaker inside and the head unit will shut down to protect itself.
Inspect the door wire harness for broken wires, chafed insulation, and failed wire splices. Be sure to look inside the rubber boot also.