I have a 1953 GMC and the ignition switch is just an on-off keyed switch. The back of the switch has the following letters B, I, A what do these stand for? Is it as simple as B-battery, I-ignition, and A-accessory. I appreciate any help as I was going to tap into the fuse block but the brake fuse is always hot and the tail light is only on with the headlight switch.