That sounds typical of a bad ignition switch or an overheated terminal in its connector. I'm sorry that I don't have access to a wiring diagram to tell for sure or to tell you wire colors, but usually all of those systems come off the same terminal on the switch. Turning on anything that draws more current will cause a voltage drop to occur across those poor contacts. The resulting lower voltage will make the radio interpret that as you turned off the ignition switch.
The place to start is by inspecting the switch connector for signs of melted plastic or blackened terminals. If none are found, test the wires for voltage. With the switch off, any with 12 volts are the feed wires. Look for those that have 12 volts only when the switch is in the "run" or "accessory" position. Of those, look for one where the voltage goes down when you switch on the heater fan or run the windows up and down. If you find a wire where the voltage goes down, check for that on the feed wires too. If you find it doing that on a feed wire, you have an overheated connector in the wires going up to the switch. If the feed wires have good voltage all the time, suspect the switch.
Dec 22, 2012 at 8:33 PM
