You can attach the lights to a Buck Converter, where you can adjust the ouput voltage, I use it set to 10 volts for the passenger cars. Here is the link for the convertors: https://www.ebay.ca/itm/162724139001, DC in and DC out, could to go I use a 2amp rectifier for DC in, then connect your lights to DC out. Adjust brightness level and your done...
Marty