Technical @$!#!! Wiring argh!

Good afternoon☺
i have been trying to wrap up my 38 ford coe build. I am at the stage now of finishing the wiring. One issue that ive been wrestling with the last day or so is wiring in my heater blower motor.
here is where i need help...i used a rear heater unit out of about an 88 or so chevy van. There are 4 wires coming out of the heater unit. White, yellow, brown, and blue. The white is grounded and also goes to the resistor, the brown goes to the motor while the yellow and blue go to the resistor.
im trying to hook this up to a 3 position switch like the one in the picture below. None of the terminals are marked on the switch.
can any of you wiring experts out there tell me how to wire this. Id like to get the dash buttoned up today if i can get this figured out.
thanks ☺

 

Get a multimeter Use the continuity function and connect to one of the contacts, take the other and go to another terminal. If they are connected internally meter will read closed (at least on mine ). Continue until you find which terminal connections to the other 3, than that is your main feed in. Than just wire it up so all 3 functions work how you want it

 

After you figure out what the switch does, you'll need to wire it. One wire should go to each terminal on the resistor, from each terminal on the switch (but not the "common" terminal. The "common" terminal should connect to power source)

I'm a bit confused when you say that the white wire is grounded, but also goes to the resistor. Maybe a picture would help.

 

GM didn't change much over many years for wiring the blower motor, you should be able to find a schematic online for something GM from the 1980s. I wired my 12v system up as GM did to the 6V heater motor on the 47 caddy and cut the leg for high speed so it would be the "off" position. Kept 3 fan speeds, all other positions go through resistors to limit the current to the motor, hasn't burned up yet.

 

Ive tried finding wiring diagrams with no luck

 

I was using my multi meter on it, couldnt figure it out

 

Here ya go, found this online, no idea what it is from but it looks GM. Regardless of what it is from you can use it to understand how the system works.





You can lose the blower motor relay and run directly to the fan motor. With this schematic you can make it work. Your blue, yellow, and white colored wires plug goes to the resistor group, just remove it (2 screws) and ohm them out one at a time and in series to figure out how to wire it for the multiple speeds. The more resistance the slower the fan speed, just like in the schematic. Switch position 1 is the slowest speed, 4 is fastest using the resistors, and 5 is direct for high speed. With a 6v motor I disconnect 5 so there is never full power sent to the motor.

DVM can be used to check the switch to figure out power in and what terminals are the outputs.

 

Note that you also need a blower motor resistor assembly as shown in the diagram. It is a rack of resistors and must be mounted in the air duct for cooling. They used the same one for years on all kinds of cars. By that I mean, an 88 Chev van used basically the same one as all GM vehicles for probably 10 years or more. So just go get one for an 88 Chev van, it will be fine.

HVAC control module = your switch. There is some extra stuff in the diagram for air conditioning or climate control or something.

Basically you need 12v power TO the resistors, the different voltages coming FROM the resistor to the switch, then TO the blower.

 

He already has the resistors, the 3 prong plug is connected to them. 2 screws and they will come out as an assembly.