I think a 50amp breaker is recommended. My Terrova 55 would trip a 40 if ran on high for any length of time. If the fuse was just a 20, I would lean toward that being the problem. Just change the fuse and hit the on button. If it comes on, shut it down and go get a 50amp breaker. Be sure you have large enough wire from the battery to the TM to carry the load.

By the time I got this typed and posted, looks like you already got this advice. With a light, it should be no trouble to find your problem.