Wiper speed?

Sounds like you may have a bad switch. 3 speed wipers did not come out until 74 and that year it was an option. the easy way to test the switch is find friend with a 70 to 73 a body and do a little plug and play. i have also found with these old cars corrosion sometimes breaks the connection at the plug in points a little Noalox on the connectors goes along way.