Calling electric gurus, help!

Brake light switch has one wire hot at all times. Pedal movement closes switch. i majority of classic vehicles, power goes through and up into the turn signal switch, typically on a white wire. Turn signal switch centered allows brake lamp power to pass to both rear fixtures on same 2 wires for used for rear turn. Signal switch moved left or right takes brake power away from one wire and sends on to one rear fixture. So... the proper turn signal switch for 2 of 1157 fixtures at rear, switch moved to left or right, should send turn signal current to 3 of the 4 wires, 2 front and only one rear.
It is possible that the switch you have belongs to a vehicle that had 4 rear lamps, probably all 1156 bulbs, 2 for brake, 2 for turn. Brake current doesn't go through this signal switch. It goes direct to 2 rear fixtures. I hope this doesn't read too complicated.