Dash and tail lights

Have you recently installed an aftermarket radio?

A lot of people make the mistake of looking for the ground wire in the radio harness. There isn't one, but if you use an ohm meter to try to figure out which one it is, you can be confused by the tail light or dash light circuits because they also measure very low resistance just like a ground wire. The original radio used the tail light circuit to tell it to dim the display and it used the dash light circuit to tell it how much to dim. When either of those wires are connected to the new radio's ground wire, that light circuit will have a short to ground through the antenna cable. To prove this, just unplug the new radio, then replace the fuse and it shouldn't blow. Cut off and tape the wire that was used as the ground, then use the braided strap that was bolted to the back of the old radio or the black wire that was clipped to the back. Connect that strap or wire to the new radio's ground wire.