Getting through the firewall...

[deermagnet]

But, I only want 1 switch, so can I splice the wires together so it can all be powered by a single switch?

Yes, you can do that with no problem. The relays draw less than one amp each. You can buy any switch you want, such as a lighted toggle and drill a hole in a blank for it. Wire the switch to both relays and you'll be drawing less than two amps thru the switch. That's the beauty of using relays. The switch never sees any of the high load needed to power the lights. Only a small current goes thru the switch to trip the relay and allow the high current to travel thru the relay only.

Maybe you could find a three-way switch. One position is off, next is one hot wire to one relay, next position is two hot wires to both relays. Your choice of two or four lights with one switch.

Also, be sure to power those relays separately. Run two wires from the battery to the relays. One wire to power all four lights would be a problem.

Mark