I've installed my boost gauge and it works great. However, I couldn't figure out what wire to tap for illumination.
I have the gauge pod from SubieGal so it sits next to the A-pillar. The wire to the gauge isn't very long so I ended up tapping the green/black wire going to the cruise control switch for 12V.
From what I understand, there is a violet and an orange/white wire going to the switch for illumination. When I test the violet wire, it provided around 11V when the lights are on. That's good, but it doesn't dim with the dimmer switch. When I test the orange/white wire, it is affected by the dimmer switch, but it's opposite. When the dimmer is set at full brightness, it puts out under .5V. When it's turned down all the way, its putting out about 11V.
So I'm guessing that you need to use these two wires together to get it to dim properly, but there's only one illumination wire on the gauge (unless that brown wire they tell you not to use is related). It's an Omori gauge, if that helps.
So... any ideas?