Weird dash illumination problem

I was fiddling around with the wires behind the coin tray to tap a ground wire for an illuminated switch, and after I was done I discovered that none of the radio or climate control lights illuminate any more. Oddly, though, the coin tray light and the "Display" button by the clock still illuminate, so it's definitely not a blown fuse on the illumination circuit. I also get power from the cigarette lighter, but no light there either.

 

I even removed the tap I had added, thinking I might have accidentally tapped the wrong wire or grounded something I shouldn't have - still no dice.

 

Any other ideas? Everything else still works fine.

 

EDIT - Also, license plate lights are out. So it looks like the entire #2 illumination circuit is out.

 

Could it be the illumination control module, or does that control something else?

Edited November 13, 2013 by Arcteryx

Weird! This should probably be in Interior/Audio section. Edited November 13, 2013 by JJr

Mods, feel free to move this as JJr suggested. Edited November 13, 2013 by Arcteryx

Check the fuses.

 

Also be aware that a lot of stuff in the cars we have do have the breakers on the ground side making the following chain: +12V => Load => Switch => Ground.

 

Replace Switch with rheostat in applicable places.

All fuses have been checked with a continuity tester.

 

I'm pretty sure I blew the BIU . Going to check it and attempt to fix it...

Do any illumination in the instrument panel work and behave when you tune the rheostat?

 

The license plate lights are on the same fuse and wire as the tail lights, so if they are dead it has to be unrelated.

 

Be aware that the BIU gets power from fuses both from the main fuse box by the battery and the fuse box in the footwell so you need to check both locations for dead fuses - and actually measure them, sometimes they can get a hairline fracture and still look right.

 

Also - toggle the parking light switch on the steering column forth and back and see if that makes any difference.

The instrument panel dims fine.

 

According to the service manual, the license plate lights are on the same circuit as (some of) the dashboard lights.

 

Yes, I've checked both fuseboxes for continuity, as I mentioned.

Checking around a bit - the BIU do work on the ground wire of the illumination devices so in case you tried to get a ground for something else on the ground side of anything illuminated it's possible that you did toast the BIU, but if some parts do change in intensity and some don't then it's not the BIU because all illumination is controlled by the same input on the BIU.

Anything else that dims outside the instrument cluster?

Also - measure the voltage to ground on both sides of one of the "offending" items. That may give a clue.

Anything else that dims outside the instrument cluster?

 

Everything dims as it should, I think - the gauges, clock, HVAC, and radio display. There's just no backlighting on the HVAC, radio, seat heater switches, cigarette lighter, or mirror controls .

 

I suppose it could also be the illumination control unit which is fried (which would be a much cheaper fix).

You may want to look here: http://legacygt.com/forums/showpost.php?p=4487789&postcount=359

 

The wiring for all 4th generation is similar, so you may be able to figure out something.

Updated: Parking lights and hazard lights work fine. No voltage measured across the cigarette lighter light.

 

Going to pull the BIU over the weekend and see if any of the FETs appear to be burned out.

 

Looking at the vacation pics, it would appear that there's no separate illumination module on this gen of Legacy - is that correct?

And what's the voltage to ground from the cigarette lighter pins? You need to find some part that is beyond doubt chassis grounded and measure against that point. The lamp shall have a voltage of 12V to true chassis ground (not across the light) when you have the parking lights on by the stalk and key on. If there's no voltage then it's on the 12V feed side the problem is and not the BIU.

 

The BIU works on the grounding side of the backlights and controls the dimming of them.

Ever figure this out? I'm dealing with the same thing now.

Ever figure this out? I'm dealing with the same thing now.

 

Yes. I'd blown the BIU somehow. I tried to fix the old one, but it's tricky because not only is the BIU very difficult to get apart, it's also hard to unsolder and solder surface-mount components.

 

It was a rather costly mistake (and a PITA, because the dealer has to setup the new BIU to match the transponder in your keys).

https://legacygt.com/forums/showthread.php/diy-05-bl-bp-stereo-heat-switches-mirror-switch-illumination-177954.html?t=177954&highlight=BIU+repair

If i jump 12v to the A5 wire will that light up the backlights?