Hey all. I have a 98 F150 4x4, 4.6, auto trans. I'm installing a trans temp gauge and instruction say:

"Connect purple wire from gauge to the night time dimming circuit. (The purple wire must be connected to the headlight switch circuit so that there are 12v to the purple wire when the headlight switch is on and no voltage when the headlight switch is off)"

Anyone know what color wire that is on the headlight switch?

 

Free wiring diagrams are available at AutoZone.com. You have to sign up to the site, but it too is free.

 

They want you to go to the dimmer switch or the dash lights, so you can dim the gauge as well should be light blue, red tracer, check fuse number 10 under dash, I think its a 4 amp you can tap right into there, if your looking for thew wire coming from the headlight switch its white with a light blue tracer

 

I would tape into any lightblue/red under the dash. They go all over the place to feed the dash lighting. The fuse box as was suggested is a good place also, I am not familiar with a 98 but all the previous trucks had a fuse just for the dashlights and it was AFTER the headlight switch, so power should go on and off at the fuse, and the dimming function should work too.