On Friday, January 31, 2014 8:38:43 PM UTC-8, Ignoramus16088 wrote:
We have a 1985' Ford LNT9000 semi tractor. Its heater used to work. It

was switched by a four position heater switch. It recently stopped

working. I just started troubleshooting this problem, and found it to

be very painful to do, due to cramped panel and complicated wiring

that is hard to access.



So far, I have been able to locate two wires that supply electricity

to the heater fan. If I apply 12v to them, the fan runs vigorously.



The truck, as far as I can see, has no fuses.



From our motor-heads, I wanted to find out what would be the most

typical issue with those fans. Maybe it can help shorten my search for

the trouble. Thanks



Here is the Motörhead help you asked for:

http://www.youtube.com/watch?v=1iwC2QljLn4