I had a jumpy tach reading, so I switched to the alternate rectifier tach output. After several hours of running, the tach again started to get jumpy, the engine lost rpm, I looked back and saw smoke coming from the motor cowling. Grabbed the fire extinguisher, but luckily the gasoline didn't ignite. The boat orginally had a two battery setup, sharing the starting battery as one of the 24v trolling motor batteries. I changed to a three battery setup shortly before the fire, but the rectifiers were probably already damaged.