Looking for a circuit

I have added a business band two radio. I have fed it from the battery thru a fuse and then thru a relay. I wanted the relay to make sure the radio did not get left on and drain the batteries. I have hunted with my meter but cannot seem to find an easy (not cut into a harness) place to access a 12 volt signal that stays on like the radio or power windows (remain on until the door is opened or until it times out).

Any Ideas of where to find it?

Thanks

I use the power window circuit for many "light demand" items (EGT amp, air bag controller, etc.). The circuit is a 25A ACB (auto Circuit Breaker) and RAP (Retained Accessory Power), so watch the required amperage, and relay if necessary. It's easily accessed at the passenger compartment fuse panel at the left end of the dash. You can either piggy-back the spade, or splice into the power window output from the panel.

Thanks, I will use that to trigger the relay.