ive got 2 100 watt off road lights wired with a fuse and relay...can i add a third light and b ok???

 

It depends on the rated capacity of the relay and the wiring. You've got a 16.7 amp draw right now with the two 100 watt lights. Remember, the entire system must be sized (and fused) properly. I've seen a correctly sized relay connected to rinky dink wiring - causing the circuit to fail. Then of course there's the old 40 amp fuse trick - which just leads to more smoke ...