Reverse lights, On in R or with switch?

I am not very familiar with relays, so hopefully you guys can help me out. I want to wire up a set of auxiliary reverse lights on my TJ, and want to have them come on in R, and also have them switched separately in case I need them hooking up a trailer or anything like that. Would I use a SPDT relay for this? And what wires would go with what connections? Or would I have to use two SPST relays?

30 - aux lights (+) 87 - constant 12V(+) 86 - chassis ground (-) 85 - to switch then to reverse light(+) - ground the aux lights (-) to chassis ground - the center pin of the relay (87a) is not needed, so get virtually any relay at your choice. In fact, you DON'T even need a relay, if the aux lights don't draw a lot of current. Just like reverse sensors, you just T the (+) to the (+) of your reverse light wire. No risk or harm to anything, no diode is needed. Just be sure to fuse accordingly. Use relay ONLY if the reverse lights or aux lights get too dim.

I plan on going with something that will probably draw too much current, like a set of fog lights, which iirc are 55w a piece. It sounds like with your plan that they would have a switch to control the lights coming on or not while I am in reverse. What I would really like to do is have them switched so that I can turn them on regardless of what gear I am in, and have them always come on in reverse.

Then try this: Relay # 1: 30 - aux lights (+) 87 - constant 12V(+) 86 - chassis ground (-) 85 - to switch then to ignition 12V(+) 87a - connects to 30 of relay2 Relay # 2: 30 - connects to 87a of relay1 87 - constant 12V(+) 86 - chassis ground (-) 85 - reverse light(+) The relay1 can only be energized when the switch is in ON position and ignition 12V(+) is supplied. Whenever in reverse position, relay2 will be energized, which in turn supply 12V(+) to 30 of relay2, then supply to 87a of relay1. When you toggle the switch to ON position, it will win and override whatever state relay2 is in. No conflict/overlap though.

Thanks bsd, that looks like exactly what I need, I'll have to wire it up this weekend.