I installed an Autometer temperarture gauges for the transmission on my MR because it over heats at the track even with the addition of SSP cooler kit. I am looking for a wire that goes from 0V to 12V when the head lights are turned on.

 

bump, good question

 

There should be a yellow dimmer wire on every aftermarket radio harness. I have one and so does my friend. Wire says "dimmer" on both of our's. (one honda one mitsu ;-) )