1989 GMC suburban blower switch rear a/c

The blower switch on my '89 suburban for the rear a/c burned out. I have replaced the switch a couple of yrs. ago, but the factory switches(plastic) are flimsy. There are 3 wires; large black(power), large red, small yellow. Right now I have a simple toggle switch(metal kind) wired to the black(power) and the red wire. The yellow wire is not connected because my toggle only has 2 spades. The rear a/c blows on HIGH when I flip the toggle, so I assume I'm powering the HIGH speed circuit. I assume the yellow wire is for the LO circuit, but I notice it is quite lighter gauge than the black wire and the red wire, so I am not sure if the yellow wire is supposed to carry voltage to the rear blower. Just wondering if the factory switch can be replaced with a simple toggle switch(metal kind), with three spades or is there something special about the plastic factory switches and how they work to send LO or HIGH voltage to the rear a/c blower. Thanks very much for any help or any idea what the yellow wire is for.

For the wiring it is best to get a good wiring diagram.
You could toggle switch it but you may not have all speeds.
MT

Confirmed- Yellow is low speed- it feeds through a resistor - at the blower motor- orange is high speed- feeds 12v directly to the blower motor- only 2 choices low or high-