The worst that happened to me with any Williams engine, the reverse board would stay locked in the direction I wanted, so I replaced it with a bridge rectifier.
John, take out the circuit boar and bypass with a bridge rectifier to see if the board is good or not. The bridge rectifier, 6 amp 50 volt, only costs around $6.00 to $8.50 at Radio Shack and is the cheapest way to test the motors without hurting them. The bridge rectifier supplies DC voltage to the motors, that is what the circuit board does as well except it has forwardand reverse and nuetral.
Lee Fritz