Phil,
Does the breaker trip before you use the trim tab switches? If so check the wire from the breaker to the trim tab switch for a short to ground. If you do not operate the trim tab switches then the power should not go further than the switches.
If it trips when you attempt to operate the trim tabs then it could be a short in the wire harness that connects the switch to the pump unit, a problem in the pump unit itself, or possibly a defective breaker.
You can try the tabs individually in different directions, this will send power down different wires in the harness to help isolate a short or problem in the pump unit. There are wires from the switch to the pump unit for pump up, pump down, port valve, and starboard valve.
The Bennett web site has troubleshooting information, installation manuals, wire color code charts, etc. I also discovered that they have a 5 year warranty.
Howard