I want to make a running light in my car so whenever the engine is running the light is on. What wire would I need to tap into to make this work?

 

Do you want it only when the engine is running or when the ignition is turned on?

 

I want it only to turn on when the engine is running.

 

You could tap into the fuel pump power wire at the relay. The pump is only on when the engine is running, or temporarily when the ignition is just turned on (engine off). With this make sure you use the signal from the relay to activate another relay for the lights so you do not put extra loading on the circuit.

Another one is from the A.I.R. diverter valve. I haven't checked it but I know that when the engine goes into closed loop the valve gets a sigal to divert air to the cat. This option would turn the lights on after the engine is in closed loop.

Ther might be other options out there too. Hope this helps,

-Ozzy