69 A100 PU Heater

When I got the truck, the heater assembly was in a cardboard box, and now I'm reconstructing it. I have a new motor (Four Seasons 35563), and core checks good, but need to figure out the switch wiring, especially the resistor (s?).

I see a switch on the front, seems to have three setting, assuming Off, Low and High. Three wires off the back, Green (power in), Red and Black. Also, only one resistor coil in the box of parts, the cardboard mount is long gone. So, I'm assuming that there's only one resistor coil, used for Low. Also, no ground wire seen, assuming the heater grounds through the mounting studs.

Does that all sound right?

Thanks much.

That sounds almost fine.

If it's three wires: one would be connected to ground (I'd assume black), one to high (I'd assume red) at the switch, and one via the resistor to low on the switch (green for the last).

To confirm, check the voltage at the two wires at the switch without the motor connected. They should provide 12V at their respective setting (Low/High). Unfortunately, the blower motor is not part of my '69 wiring diagram and the Accessory section of my service manual has no wiring shown either. Also, check by just shortly connecting the three wires at the motor to a battery, that the motor is running at the respective wires - not that you'll create a short with much more  damage possible.

I forgot to take pictures when I opened my heater box (all was working and dry), but some fellow might chime in.

Oh, reading right is helpful. Forget my post above!

The switch is connected to 12V+ (IGN) on the black wire (at least to what my wiring diagram shows) directly to the fuse panel (maybe with a connector). Then, the other two wires go to the heater box. One for high, one for low. GND provided via the studs.

So, your thought was perfectly fine.