Thanks Jeff.

The car had been sitting since 1978 when I bought it in 2020. I have already replaced the circuit board since the original was pretty crunchy. I tested everything and replaced several rusted/broken light sockets, secured electrical connections, put in a separate ground wire, etc. Everything seems to work now as it should except the dull glow. I ordered the new Brake Distribution Switch this morning and will update after I get it installed. I've got to think that the switch has some sort of short to ground somewhere in it since the light comes on very bright when I ground the wire and the only way to get the light to go completely out is to unplug that wire from the switch. Thanks again for your suggestion.