What relay can I use to wire to my stereo rocker switch on my rocker panel? I'm just looking for a simple relay so I can run a direct wire for my head unit to the battery switch.

Any will work. Just go to AutoZone and pick up a relay for foglights. Why the need to use a relay instead of using the rocker for just the head unit?

Hmmm... I guess you are right. I could wire the positive lead directly from the battery switch terminal to the rocker and then from the rocker to the stereo. But right now the rocker is part of the fuse panel and when I turn on the blowers or play the stereo too loud, there is a voltage drop from the rocker switch and that causes my head unit to momentarily shut down. I had the same problems in my other bajas as well. So I was planning on running a positive lead from the battery switch to the relay and control the relay with the rocker. I feel like that is the least amount of wiring.

Most head units have a Constant Power (yellow) wire and a Switched Power (red) wire in the harness. The yellow goes to +12v constant and the red wire goes to a switch or ignition and just turns on the radio (like an amp remote wire). I have seen many times in boats these get tied together. You likely would not need to add a relay if this is the case. Just separate the two respectively.

My head unit does have a yellow (power/memory) wire and a red (switched power) wire in the harness. And both wires were basically tied together because they were both connected to the stereo switch in the dash panel via a red and yellow wire from the switch. I really don't know how much power the head unit draws from the yellow when it's turned off, but I did not want any power drawn from the batteries if I had the stereo switch turned off. So I decided to use a relay for the yellow wire that is connected from the battery switch terminal to the yellow wire for the head unit. The yellow wire from the stereo switch controls the relay. This is working good for me now. I guess if I decide that I want to keep the clock and my sound settings with the stereo switch off, I could remove the relay.