72 Cutlass - unmolested wiring...BUT, high speed blower no workie.
I checked every relay, every sensor and resistor (replaced reisitor with new for troubleshooting) and found nothing wrong but could not figure out how to test the blower switch. Gave up and bought a new switch. Waiting for delivery.

Anyone know what the light green wire to the blower switch does? Removing it from the switch changed nothing...nada.

 

Typically the problem described is the blower resistor. It can fail on any of the fan speed settings. Not usually the switch.

 

As mentioned in my post, the resistor was replaced with new.

 

Did you check the wiring for continuity/power going to the relay/resistor???

 

Yes, saw that. I was just saying what it typically is. Hopefully it's the switch, but if not you'll have to test your wiring back to the blower relay. The question about the green wire? According to the 72 CSM the wires on the switch connector are brown, yellow and red/w white stripe. The latter being your high speed fan.

 

Yep, all checked good.

 

Classic Car Wiring Schematic shows different colors than your 72 CSM and they match what's in my car

 

I'm guessing it is used on a 72'...someone please correct if not...is the inline fuse good?

 

Go figure. I've always trusted the CSM for it's information. That doesn't look like the diagram in the CSM except for the mass of colored lines.

Ok, here's some other info to consider:
Check 30 amp in line fuse, junction block to hi blower relay
If its blown, replace. If it blows again you likely have a short in the wire from the fuse to the hi power relay. Repair and replace the fuse again.
If it still doesn't work - replace the high speed relay (but you said you already confirmed it's ok??)

If the fuse is ok
put the speed switch to HI. connect a 12V to the black orange stripe wire at the blower relay. If nothing - replace the relay.

If high speed works, connect a 12 test light to ground and first to the black-orange wire on the relay, then same wire on the high speed fan switch. If the light stays off in both positions - it's the switch. If the test light is on at the switch, you have an open circuit to repair on the black/orange wire between the speed switch to the relay.

 

MY BAD !!!
I concluded that the blower motor relay was good since I could hear it click on. I put a new relay on it and all blower speeds now work.

Just for future reference
The High Speed circuit of the blower motor bypasses the blower resistor module which only controls speeds 1, 2 and 3. The blower relay toggles the speed circuit between the resistor and the resistor bypass.

 

Isn't there an inline fuse? The reason I ask, is I had a fire in a 69 when some P.O yahoo didn't install the inline fuse

 

Yes. between the horn relay junction block and the blower relay. The OEM fuse was a 1/2" long glass fuse inside a cylindrical rubber holder. (I think it's supposed to be 30 amp but I replaced it with a 15 amp for now) That wire is ALWAYS HOT - UNSWITCHED.

There is also a fusible link at the compressor clutch connector.

 

I remember it being a 30 Amp fuse. Hopefully someone with documentation can verify this.