88 GTA, stock radio, the backlighting does not work when headlights/parking light switch is turned on. Previous owner had installed a jumper from brown wire to grey wire at the radio. At the time backlighting worked. The wiring job was crap, could have caused a potential short, so I removed the jumper and re-spliced the wires to there appropriate wire and no jumpers. checked voltage at brown wire on the back of radio with dim switch to max and I have 12 volts. check voltage on grey wire, no voltage. the inst pl fuse is good. The grey wire continuity checks good from the radio to the dim switch. forgot to check continuity to the headlight/ parking lamp switch, will check that tonight if there is supposed to be a connection there. Here's an odd thing, when I check voltage with my voltmeter at the fuse, fuse removed, there's' nothing. put fuse in, and check for voltage with one of those fuse checker tools that has a light. the light comes on indicating there's power flowing, not sure if i have a good connection in the fuse panel though. had to wiggle and push with some force to get any results from the checker. So where does the inst pl fuse get its power from? is there a fusible link somewhere? what else can I check and test to get power to the grey wire? Id like to get back lighting working correctly. Contemplating puling fuse block down and verifying wire color and integrity of the wires at the fuse block. Is the power at the inst pl fuse a constant power, or is just a switched power? Id think it would be a constant power, but I don't have the manual in front of me right now since I'm at work. Any suggestion on what to troubleshoot next is greatly appreciated.

 

It looks like the problem with no backlight on the stereo is due to a lack of power on the gray wire. You need to check the continuity of the headlight/parking light switch circuit to see if there is a connection there. If there is a connection there, then you need to check the continuity of the gray wire from the mag to the light switch. You can also check the fuse box and make sure the color and continuity of the wires in the fuse box are in place. Regarding the fuse link: a fuse link is a special type of fuse that is designed to quickly trip the circuit when the load exceeds the allowable load. If the fusible link blows, it indicates a problem in the circuit and must be replaced with a new one. Regarding constant power: there are usually two power wires on a mag - constant power (usually red) and switched power (usually yellow). Constant power provides constant power to keep the settings and other information on the boombox, even when the car is turned off. Commutated power, on the other hand, is only supplied when the car's ignition is on.

 

I have continuity from the radio to headlight/parking light switch. what is the mag you mentioned?