circuit that only on when engine is running???

I'm in the process of installing a pusher type fuel pump. I'm running Vege oil and want to take the extra strain off the injector fuel pump.

I am trying to figure out the best place to tap into to trigger a relay??? I need to find a circuit that is only on when the engine is running.

I was going to tap into the fuel heater on top of the fuel filter but it occurred to me that it may shut off at given engine temp???

Any suggestions? Ideally a circuit that is relatively easy to find in area of the engine or towards the back of the vehicle.

Cheers.

The answer was.... the A/C. The AC fusable link in directly below the glove box and easy to tap into.

Pump is in and pushing strong. Much more pep above 3000 rpms.

Good job