I had a similar problem with my PP all summer. I sent it back to PP and all checked out okay. This past weekend I finally figured out what the problem was..... it was the main power wire from the boat to the ignition, not the PP wire to the ignition.
I had always checked the PP wires for a loose connection and not the boat's power wires. I would have thought that if the problem was a loose wire on the boat side other instruments would be cycling on and off as well. I was wrong, because I discovered that the power wire going from the boat's power to the ignition was loose. When I jiggled it the PP would turn off and on, even though the power wire from PP to the ignition was a solid connection. I tightened up the other wire and now all is fine.