Cab blower fan on my 4960 didnt start the other day. I pulled the blower fan out and it will run directly hooked to 12v battery and sounds fine. I did install new switch and resistor to eliminate as culprits. At the connection going to the blower I have 12 volts ….. that is UNTIL I hook the motor to the leads and then voltage drops to 0. I'm out of my element here. What else can I check?