ddalesr3 has hit it right on the head. Many vendors sell an after-market 12 volt electric wiper motor for 6 volt trucks. The level of performance is diminished.

Also, all after-market electric wiper motors for 54/55 trucks will not work with a stock or reproduction 54/55 radio.

1954 was the first year for a GM accessory 6v 2-speed electric wiper motor. It fit in fine with a stock radio/speaker. They are hard to find, however.

Tim