Your issue could be a few things electrical that you have been chasing down. Since your boat is a classic it leads me to believe your windless is an older version as well. You could possibly have a large buildup of crud and such in the gears. A while back there was no gasket seal between the housing plate and the windless body and salt water intrusion caused a mess. A couple of us had to bite the bullet and replace the unit. Can you turn the unit freely manually? If so it could be a shot motor. Here is Lewmar's meager troubleshooting guide:
1.Anchor rode pays out independently while windlass is not in use.
• This problem is a result of not securing the anchor rode combined with the gypsy drive cap being
slack. Tighten the gypsy drive cap using the winch handle and always secure the anchor rode
independently of the windlass when not in use.
2.Failure to operate or sluggish operation.
• The majority of these problems are electrical in nature. It is essential that the proper voltage be
maintained. The proper voltage on a 12 Volt system is 13.5 Volts, constant low voltage will damage
motor.
Ensure electrical cable size is large enough to handle the current draw and keep voltage drop within
acceptable limits.
• Check control switches, connections, battery condition, isolator switch, fuse and motor for
operation failure.
3.Failure to operate.
• Is there a voltage at the input terminals to the contactor and switches. Check the circuit breaker/
isolator switch and any fuses.
• Operate the switch. Is there voltage at the positive switch terminal on the solenoid. If not, the switch
(or its wiring), is difective.
• Keep the switch activated. Is there voltage at the main output terminal on the contactor. If not check
the contactor coil ground circuit. If okay, replace the contactor.
• Check the voltage at the motor. If voltage of at least 12.5 volts is present and the motor does not
operate, the motor is defective.
8