I need a wire to draw power from to throw a relay when the engine is running.

I have a York belt driven compressor (on board air) with a magnetic clutch. I want to make it impossible to drain the battery by leaving the clutch magnetized with the engine off. Thus, I want to find an easy-to-access wire that is hot ONLY when the engine is running.

The only option I've thought of, that's easy to get to is the daytime-running-light circuit.

 

Only when the engine is running or only when the key is in the right most position? If it is the 2nd then if you feel like fishing a wire through the firewall you could pig tail off of the back side of the cig lighter - the main wiring harness isn't too hard to get to either. You just take off the few screws and the 10mm bolt under the steering column. You could easily find a keyed wire there.

Or were you hoping to locate one under the hood?

 

Ideally under the hood, cause that makes my life easy.

 

Pull power from the fuse box. The Black/yellow, and Black/orange wires should be powered only when the key is in the accessory and on position.

 

I didn't know that colour code was in effect, that's awesome.

 

or, you could always just pull from the stereo harness...

 

I think all toyotas use the same wiring colors

 

It's a pain in the butt to pull wires through the firewall. I like the fuse box idea better.