Did you guys look here?
Creating a List of Electronics Projects developed on the OGR Forum
Specifically, for passenger car lighting...
https://ogrforum.ogaugerr.com/...ighting-module-files
Or if you prefer constant voltage, a variation on that board.
https://ogrforum.ogaugerr.com/...t-module-build-files
Here's a link to a large post with a host of useful DIY electronic projects.