You guys ever dealt with a system that hooks the positive side of the battery to ground and then the negative side of the battery to your wiring harness? Crazy! Been helping a friend get a 1960 MG started that has been sitting for 15 years. His brother died a few years back and the car had been sitting for along time prior to that. I went thru entire fuel system, brakes, etc.... Engine would turn over but would not get any spark. I start getting into the ignition system and I find that the + side of the coil ran to ground. I'm thinking, Oh I have the issue, coil is backwards. All the muscle cars I have worked on run 12v to the Positive side of coil and then the negative goes to the points in the distributor. Point close, Coil energizes, points open up and bam, spark to spark plugs. So I flip this thing around and still nothing. I ask my friend, "was you brother bright or just the type that hooked things up till it worked?". he said, no he knew his stuff. I said well we got to assume what your brother did was right. The I start researching and I find that many cars up to the 50's and 60's used positive ground systems. Which is crazy. What I am saying is that you can install the battery in your car either way and the car will still turn over. The headlights will work and other things that aren't polarized will work. But things like the radio and ignition which are polarized won't work. The ignition coil is wound in a certain direction and has to be wired based on which battery polarization you are using. So thinking things thru, I remember my friend telling me a few years back a new battery was installed and they tried to start car. The battery was installed negative ground. So with some trepidation, I reversed the battery cables and put the positive to ground. turn the engine over and Bam, it started after 15 years. You never stop learning. Apparently in the same year in the 50's, Chevrolet was positive ground and GMC was negative ground.