Positive ground or incompetent owner?
I just bought a 1975 Newport 28, which came with one battery in place, but two extras that the owner had never hooked up. The battery compartment is under the starboard settee with the AB switch mounted close by under the navigation table. I looked over the connections to see where everything went, and I had to look twice to make sure I was seeing right.
The AB switch has two red cables, at 5 and 7 o'clock, and a black cable at 6 o'clock. The black cable leads to the positive terminal on the battery, and the 7 o'clock red lead runs out of sight into the engine compartment. There is another red lead coming back from the engine compartment and is connected to the negative terminal of the battery. The battery provides power when the switch is set to B.
My first guess was that someone had misconfigured the AB switch, and used the wrong color wires to boot, as I'd figure the two red leads would go to battery positives, the middle 6 o'clock lead would be red as well, and lead to the bus, and a black cable would come back from the ground to the negative terminal.
However, a friend suggested that it might be a positive ground system, which seems odd for an American-built boat from 1975. I haven't had time to really look around yet, just sticking my head into an access panel, but it seems to me I've seen at least one other black lead going to ground.
Still, it all means I'm going to have to spend time tracking down those leads to see where they go, instead of just hooking up new batteries. Is there any real chance this might be a positive ground electrical system?