86 country squire with ATC

I have an intermittent problem with the Fan not coming on for heat or A/C. I can never get home in time to check to see if there is voltage to the Fan. It just comes on when it wants too. Then it works for a couple of weeks. Any ideas out there???/ thanks Arne

They have a resistor for blower speeds normally when this goes bad it will work on high speed without the resistor. Located near the blower motor in the heater case usually near the fire wall.
Check the ground it may be loose. Check for a loose connection.

I have multiple speeds. Is there a separate ground????? I just see a connector going to the motor? Thanks Arne