I found someone who had done exactly what I wanted to do, but way back in 1984, when my truck and the C64 were new. If I can track down the software, I can use it, Otherwise, I have to make it all myself. I'm not great at programming, and this articel hints at using assembly language, which I have never used. It's a good start, as it proves what I wish to do is possible.

https://www.commodore.ca/commodore-gallery/commodore-64-car-pilot-1984-worlds-first-consumer-gps/