12v source only when headlights are on

[dnehthend]

Where can I get one? The SCIL seems to be the best place I can think of. I don't want to have to test all of the wires, anyone know which one I should use?

I need it to trigger the dim function of the gauge I'm putting in.

 

[96hotrodlincoln]

You could tap into the light for the ashtray, that's what I did for dimming my head unit since it needed a 12 V input.