[joe231]

I agree, in my experience the old corroded switches are usually the culprit. Disassemble, clean the contacts and apply a good dielectric lube on them. Don't forget to clean the connectors and pins on the back of the switch. A little dielectric there helps too. You might even need to bend the contacts in the connectors to make better connections also. Corrosion at any of the connections will drop the voltage that actually makes it to the motors. You can even replace brushes in the motors and clean the commutator while apart. It's not extremely difficult, just takes some patience. All these things need maintenance, but most never receive any attention.