They are all 12vdc, and many times they are connected with the 12V source one to the other, spliced along the way. So a bad splice at the first one can take out the others. Most often there is a switch near the entrance, and one near the bed. No breakers, but you do have a fuse in the power distribution panel for the 12VDC (usually ATC type).
My suggestion; If the fuse is good, and switches appear good, pull down one of the lights and start inspecting wires / splices. One light at a time. Good luck.