If you look on some of the trailer wiring threads you'll see where some people have tried to tap into the back taillights for a trailer and found that it triggers the External Lamps bad on the message center.

So if you wanted to do this I'd recommend using one of the modulite converters e-trailer has. It attaches to the battery and takes its power from there. It only uses the input wires to sense when then turn on and doesn't draw power. The modulite is really designed to hook up to a 4 wire trailer system but if you just wanted another tail light it should be pretty simple to tap the right wire coming out BUT the hitch covers you pointed out, they actually hook up TO the 4-wire plug that goes to a trailer... and would plug right in.

Now you can either cut your wiring harness and wire the modulite directly into the system OR you can get one of their T harnesses that hooks in series with a tail light and has a 4 wire output... you plug the 4 wire into the modulite and the output of the modulite is a fully powered plug.

Does that make sense? I have a T on order myself and a modulite. The T is on backorder. Make sure you get the right T if you get one... the FEH and the Mariner use different T harnesses because one has separate turn signals and the other doesn't.

By the way... my solution was to buy some of the 3M reflecting tape they make for trailers and put it on one of the bars so it faces back when the rack is folded and when its down. The stuff is incredibly bright. Its the same stuff you see on the back of semi tralers that alternates red/white. If you ahve some of that on there... trust me, they are going to see you!

I'm getting the wiring harness in case I ever do hook up a trailer.