[rotorwrench]

These old designs didn't have provisions for circuit protective devices like a simple glass fuse. Some folks add one at the starter power connection where the small wire attaches then goes on to attach to the amp meter. A lot of folks disconnected the battery when not using the vehicle. The large cut off switches were used to make the disconnect a lot less troublesome. Less sparking occurs if the ground cable is disconnected.

The light switch should only affect the running lights of the vehicle. The brake light circuit is a separate circuit that draws power even if the light switch is off. My guess on the brake light that comes on with the switch is that the wiring is crossed on that lamp assembly or there is a cross short between wires in the harness. A lot of folks add the second tail light for safety purposes. It was still normal to have a single tail light in that era.

Brake light switches for the 30 & 31 cars fit to the center cross member and are a pull type switch. The 28 & 29 cars mounted it in a more weather protected area so there can be problems with these switches due to that. As was mentioned, the reproduction switches are problematic due to lack of quality in manufacture so this doesn't help. A&L is the only manufacturer that tries to manufacture a working switch for the 30/31 model As. They are available from most restoration parts sources for the model A and a priced around $50. If they go bad, A&L will stand behind their product by all accounts.