I just picked up a 50 lincoln that is 6v with positive ground. My 40 Plymouth was the same way so it wasn't anything new. It's been cranking insanely slow and is hard to start because of it so I looked and the last owner put a new 6v battery in but it's hooked up negative ground but since he used 2 red battery cables I never noticed. Could that explain my slow crank? Also before I noticed it was backwards I checked the voltage when it was running and was only getting like 6.5 volts at the battery, could that be related too? Can I just switch the battery back around or do I need to do something else too?