Are you familiar with hooking up indiglo gauges? I would put it to that same wire. On my car, I think it is a red/blk wire. You also can take out your gauges and test each wire with a probe to see which one is getting current only when the dash lights come on. h: If you do a search on how to wire up indiglo gauges, you will probably find that wire. I just leave that wire connected to nothing on my stereos. What does it actually do?