Fairtax4me Posted July 18, 2012 Share Posted July 18, 2012 I don't know if this has been covered, I tried to search and didn't find anything except posts about wasted illumination control modules. Many aftermarket head units have a dimmer feature when you turn the lights on, but, as some people have found out the hard way, it can't be hooked up in a modern Subaru. That's not entirely true though. What I mean by that is it can't be hooked up to the factory radio harness dimmer wires. The reason why is those wires go to the Illumination Control Module under the dash, and the module controls power and ground for all of the dash lighting in some convoluted way. If you try to tap into the illumination circuit for power, the module shorts, the magic smoke escapes, and then you get no lights at all. You need 12v when the lights are switched on to make the dimmer work. You can't get that from the headlight switch on the stalk, because like all of the interior lights, that switch controls the ground side of the circuit, and it grounds through the ICM. The best way I figured to get the right voltage and not risk blowing up the ICM was to tap into the wiring for the exterior lights where it exits the dash fuse panel. On my 96 Legacy fuse number 5 is for the tail lights. The wire coming out of the panel is Red, and I found it on the lower right pin of the grey connector that is top left corner of the fuse panel cover. Pictured here: The multimeter probe is pointing at the wire I used. I get 12v there when the lights are switched on, and my head unit dims now! So there you have it. A simple workaround for a stupid problem! Link to comment Share on other sites More sharing options...
nipper Posted July 19, 2012 Share Posted July 19, 2012 Some units are just looking for a signal, some are actually illuminating the units. The 2nd one makes the magic smoke appear. I just tapped into the lead to the glovebox myself since that light only comes on with the lights. Link to comment Share on other sites More sharing options...
Fairtax4me Posted July 20, 2012 Author Share Posted July 20, 2012 Didn't know the glove box light was dependent on the light switch. Figured that would just be hot with key On. The longer I look at the wire diagrams the more confused I get. In some way or other, all of the lighting is tied back to the ICM. I'd like to find an explanation of exactly how that crazy thing works. Link to comment Share on other sites More sharing options...
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