Just received a very polite and prompt response from technical support at Caerbont: "Unfortunately the 3 wheeler speedo isn't manufactured by us. It's made by VDO."

He suggested contacting Mark Baldwin at Morgan. Anyone know the best way to try to get a request into him, or it it's worth trying?

Or if anyone has an idea of what the VDO speedo model # is, perhaps the technical documentation on it can be found.