In Reply to: 12 volt conversion posted by Steve on September 21, 2018 at 07:40:21:
First off, Welcome to the board! 13.5 volts tells me you have a bad ground somewhere.
Perhaps even a weak batt connection. I usually remove ground and power wires and clean everything up so it is shiny before final assembly. Just 'looking clean' might be a problem.
Good place to start. After it's cleaned up a light coat of oil can prevent future corrosion.