Now lets fix this puppy!
The glove box light also is fed from this circuit, but it is not controlled by the dimmer. If that light works, that takes care of the positive side of the circuit. The 12 volts comes from the tail lamp relay, so according to my diagram, you won't have a glove box light unless the running / tail lights are turned on.
The rheostat is an electronic module, but it still can be bypassed. We just need the right wire. You should have a green wire. That's the 12 volts that comes from the tail lamp relay. The white / black wire is the ground wire. The white / green is the ground wire for the lamps, but it goes through the dimmer module first on its way to ground. If you want to bypass the module to see if everything else works, either connect the white / black wire to the white / green wire, or just use a jumper wire to ground the white / green to the body.
If the lights turn on, the dimmer module must be replaced, but be sure that 12 volts is there on the green wire. It won't work if that's missing.
If you had found that 12 volt wire previously, what may have confused the issue is the dimmer is in the ground side of the circuit, not in the positive side like they used to do. The fact there's a 12 volt wire adds to the misery.
If the fuse blows when you ground the white / green wire, one of the bulbs, (sockets) is shorted, and logic would dictate it's related to the radio that was in there. The original radio most likely had two lamp wires. One was hooked to the tail lights to make the display dim. The second one was hooked to the dash light circuit to tell the display how much to dim. If someone reconnected those wires incorrectly, it is possible the tail lamp / dash lamp 12 volt supply got connected to the ground side of the lamps. That short may not cause the fuse to blow with the dimmer in the circuit, but it would if it was bypassed. This is a good suspect if the previous owner hacked off the radio's plug and spliced in the new wires. If an adapter harness was used, it's doubtful removing it is causing this problem.
One more tidbit of value. If the previous owner spliced wires for the radio, and sealed them with electrical tape, that can unravel into a gooey mess on a hot day. The dash is made of plastic, but if a bare wire touches the case of the radio, that is grounded, and a bare wire will be grounded if they touch.
To back up for a minute, with the dimmer still unplugged, and with the lights turned on, you should measure 12 volts on the white / green wire too. If you have that, nothing on that line can be grounded or open. At that point everything points to the dimmer module.
Monday, November 16th, 2015 AT 3:53 PM