I am posting this in the hopes it will save someone time troubleshooting a battery drain problem. I started having an issue with the battery draining after I had a dual bowl master cylinder from CJ Pony Parts installed on my '66 289 Coupe.
I TOLD THE COMPANY TO USE THE ORIGINAL PUSH ROD, AND THEY USED THE NEW ONE THAT IS NOT THE RIGHT SIZE.
The brakes work fine, but the wrong push rod is putting just enough pressure on the switch that it is slowly draining the battery without providing enough power to actually activate the lights. I ran an Ohm test and you can see the circuit complete as you let go of the brake pedal and let it rest naturally.
Does anyone know if you can adjust the brake light switch, or do I need to get a stock push rod for a '66 and re-install it? How frustrating....