I have checked every connection point I know of and all seems well.
I have 14+ volts on red at 3 pin and fusable link when running.
I have variable volts on yellow depending on speed; 4+low/4+auto/9+high.

New Ign. switch.
new blower reg. last year
new blower yesterday

The only way the heater will work is if, when the key is in the on position with the heater on. I unplug the 3 pin connector wait 5 or 10 seconds, plug it back in.
Instantly blows!
Turn the key off.
Won't work.
I feel like I have followed the chain all the way down to blower reg.(which blows when Blue is grounded). All of your advice is greatly appreciated!