I bought one of these
https://www.yellr.com/yb_home.htm nearly 15 years ago.
1980's legally-mandated speedo optimism with a tyre size/wheel change == insanely inaccurate readings.
Ready-made harnesses for popular vehicles; but only power +/- speed signal in/out so not brain surgery to use the generic unterminated harness and add connectors.
Fitted, calibrated against GPS (it needed a tad more than I'd calculated/measured). Forgot it was there because it Just Works...