1982 Plymouth Horizon Repair Question
I need a electrical wiring schematic to troubleshoot "short" from fuse panel. Keeps blowing fuse to brake lights.
You mentioned a lot of fixes but no symptoms other than the blown fuse. First of all, be aware that if you installed an aftermarket radio, there is no ground wire in the wiring harness if it had the black and gray twin 7-pin connectors. (Not sure if they had them already in '82). If you use an ohm meter to find what you think is a ground wire, you're going to find the wire for the running lights, (tells the radio's display to dim), or you'll find the wire to the dash lights, (tells the display how much to dim). They will both measure very low resistance because of all the bulbs in those circuits. Unplug the radio to see if the fuse still blows. If it doesn't, remove the wire you're using for the ground and look for the original braided strap, or run a new ground wire. The radio will also get a ground through the antenna cable but that's a very poor ground.
A simple trick to finding a short is to replace the blown fuse with a pair of spade terminals, then use small jumper wires to connect them to a 12 volt light bulb. A brake light bulb works well. When the circuit is live and the short is present, the bulb will be full brightness and hot so be sure it's not laying on the carpet or against a plastic door panel. Now you can unplug electrical connectors and move things around to see what makes the short go away. When it does, the bulb will get dim or go out.
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