I bought some small lights that I want to mount in the back of the truck that will turn on when I'm in reverse since I tinted my tails and I barely have back up light.

Is it as easy as finding the wire that goes to the reverse light now and just taping into them? Or would I also need to ground both the lights?

I'm use to wiring lights up from the battery and with a switch, not taping into other wires for the source.

If anyone can help that would be great and also what wires would I need to use and what color are they?

 

I made an adapter for my 4 pin pigtail from a $1 extender I picked up at the flea market, so the trailer reverse turns them on and off.
I went so far as to install a switch connected to the running light wire so if I needed light behind the truck to do something, I could also have light by turning my running lights on. For use as added reverse lights only, I just keep the switch turned off.

Thisaway, when trailering, I just unplug the adapter and plug my trailer pigtail in. Fifteen minute job and like I said, I had a buck in it (plus the lights)...

 

Very nice Hammer great idea there, and I bought those same lights.

But what how could I tap into the trailer wires without a adapter? Could I just use those quick tap things and find the wire that turns on the reverse lights? Did you also have to ground the lights?

 

yeah, I don't see why you can't just use the crimp type connector and tap into the reverse lights.
I did it this way because I wanted the addition of switched lights so I could see to do things behind the truck at night. Of course without running a dedicated "hot" wire, my driving lights have to be switched on to use it, but for the few minutes at a time I'd need them, I didn't see it as a big deal, especially since as soon as I can get around to it, I'm going to a dual battery setup.

I just used trailer ground (white wire in the pigtail) to ground mine. You could ground them to the chassis...

I fused mine at 10A, I'd suggest you fuse yours as well. You can see the clear plastic inline in my first pic, right before the plug.