Car Alarms: relay question, restoration shop, hearse

Question
I work for a car restoration shop and we are finishing up a 53 Hearse, the owner want the back up lights to come on when the rear door is opened so the back up and interior lights will be on at the same time. My problem is that the interior lights is a ground activated circuit and the back up lights are a power activated circuit. I need the back up lights to work normally also. Can i trigger the back up lights with a relay to do what I want? Is there a special type of relay to use?
Thanks for your time

Answer
Ok, let's try this.
wire up a relay as a negative type.
(see at www.relayhelp.com) ,
then using the reverse lights as
a trigger on pin 86, then your pin 30
would go to the ground activated circuit,
thus turning it on when in reverse.

Fuse the constant source at 10amps please.

Let me know if it did the do.

A.