I cannot find an actual diagram, however the wire from the light goes through the firewall and then connects to a wire coming from the transmission reverse light switch. The plug on the trans can be installed in 2 ways, if you have it wrong the back up lights and the dash reverse light will be on all the time. It is a simple circuit, basically one side of the switch it power, when the trans in placed into reverse it connects the power side and the light side thus energizing the back up (an reverse) lights. If you dont have a wire, you can tap into the the light side of the switch.