I am trying to clean all my wire jobs up this weekend I wanna hook my temp and oil gauge wies like it say

Here is what the intructions say

"Connect purple wire from gauge to the nighttime 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"

Which wire color wire will the purple wire need to go into?

Some said to use the wire on the radio harness anyone know what color wire it is for sure.

 

Light blue/red in the radio harness is from the dimming circuit. Voltage will vary with the dimming wheel position but it will be off when the headlight switch is off.