Do all A/C cars have a relay for the blower motor & is it mounted on the firewall? My blower works only when jumped out to battery or otherwise nothing. The plug going into the fan switch is a little burnt as well . Can resistor on box cause this & easy way to check this?
IT seems like a 50/50 split from the photos and lit I have been reading at least on the 68/69 cars . If not on the firewall any other locations come to mind, I don't see one that size in the dash ?ou:
https://www.opgi.com/skylark/BR02503/ That's the relay for a '69. Note the same firewall location as '70.
Check the high speed relay and the connectors to it on the firewall. As I recall both the low and high speed circuits run to this relay. If the issue is not there, look to the switch on the dash. A faulty resistor array should only affect the lower speeds and not the high fan speed.