How to install blower motor relays??

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I was getting a feedback loop through the "High" dark green wire that wasn't allowing the relay to turn off so I think a 20A diode there will fix it, since if I pull the dark green wire off of the resistor pack, everything works great.
 
You guys did a good analysis of the existing wiring. Another important point that you mention is that on high speed, the vacuum switch also has full current flowing through it, so it needs to be protected too with a relay.

I went out and tried my fan and it works fine on all three speeds, but maybe this is a "heads up" warning.
 
I'm having a hard time coming up with a way to keep the existing 2 way wiring, one that goes through the A/C-Max A/C and the one that goes through the Heat/Def. Where I currently have my relay, just downstream of the L-M-H switch but before the 3 prong connector won't work when I put it on Heat/Def because the current is routed an entirely different way so that even on high, it goes through 1 of the resistor coils. The only way I can see it working is by splicing the heater switch wire into the A/C wire and just having a single L-M-H speeds instead of a Heat L-M-H and an A/C L-M-H. That is without using like 14 relays and having a convoluted mess of spaghetti.
 
Again, I don't have the hardware to mess with this. You might need to get "creative." Maybe use steering diodes in combo with the resistor / switch to shut off one relay to energize the other.

Tell you what, can you give me a functional truth table for that switch? That is, what contacts make when?
 
Sorry to dig up an old thread. Just thought I add some info.
Just doing research in to updating my 65 coronet and 66 valiant blower motor with a relay. On another site it recommended using a single five pin relay right before the motor. This allows the switch and resistor like normal until HI speed is engaged then the relay supply's direct power to the motor. Blower motor wiring diagrams

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The 1962 Master tech service book session 174 Air- Conditioned car comfort. Has a diagram that shows a relay for the compressor clutch.
https://www.web.imperialclub.info/Repair/Lit/Master/174/index.htm

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I am gonna hope to get this added to my mopar to keep them working care free for years to come.
 
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