Here are three different wiring diagrams for wiring an extra set of backup light such that they can be activated by the OEM installed backup lamps OR an accessory switch:

The first one shows power from the battery running directly thru the SPST switch, which is OK as long as the switch is properly rated for the amperage.

The second one shows the use of two relays, with a diode coming off terminal 86 of the top relay. This diode should prevent power from routing backward thru the vehicle's OEM wiring if the circuit is energized with the switch.

The third diagram is almost the same as the second one, except there are no diodes. The relays have an internal coil to prevent back feed.

A few questions:

1. In diagram two, wouldn't it be a good idea to also add a diode to terminal 86 of the relay controled by the switch to prevent back feed to the switch circuit when the the lights are energized by the top relay?

2. Can someone provide part numbers and possible sources for the relays in diagram 2?

3. Will the relays depicted in the third diagram really prevent back feed?.

4. Can someone provide part numbers and possible sources for the relays in diagram 3?

Thanks!

MB