Blower motor keeps blowing fuse

[gglithox]

Having a problem with the blower motor blowing the fuse on my 1986 M1028. This problem just started yesterday, before that blower worked normally at all speeds. Now when I turn the blower on with the truck running the fuse blows and the Gen 1 light comes on. When I turn the blower switch off the Gen 1 light goes off. I am confused after reading some threads about blower motor issues, sounds like it could be a motor, resistor or alternator problem. Some advise would be appreciated.

 

[idM1028]

You've got a short somewhere in your system, more than likely in the circuit for the blower motor. Could be bad wiring, but sometimes components can short out as well (in which case they will show zero resistance on a voltmeter) Also, the GEN1 light is fused off of the heater blow motor fuse, so that explains why your GEN light is coming on.

 

[GreenBull]

Having a problem with the blower motor blowing the fuse on my 1986 M1028. This problem just started yesterday, before that blower worked normally at all speeds. Now when I turn the blower on with the truck running the fuse blows and the Gen 1 light comes on. When I turn the blower switch off the Gen 1 light goes off. I am confused after reading some threads about blower motor issues, sounds like it could be a motor, resistor or alternator problem. Some advise would be appreciated.

Step #1 for all CUCV electrical issues is the fuse panel. Pull the fuses and look how nasty the terminal blades of each fuse are. Each corroded fuse is a potential heating element that WILL cause problems.

My Recommendation is to replace each and every fuse and give your fuse panel a clean and adjust. This will remove 99% of the electrical gremlins. Pull a fuse and look. Most have corrosion at all points except those in a direct metal to metal contact. Contact cleaner, tarnex or penetrating oil soak followed by brake/contact cleaner and compressed air are the best methods. Adjustment is done with a small pick or dental tool to increase the terminal to fuse tension. After that the electrical issues are straight forward.

Blown fuses are either over current or STG. The fuse panel resistive connection issue I've described is the most common source of over current in CUCVs I’ve seen. Shorts to ground are just a matter of finding grounded wires or shorted component.

 

[dependable]

Also check the resistor. It is on passenger side firewall behind battery. Could be grounded to cab by rust, mouse debris ect.

 

[gglithox]

Thanks for the info, I will start looking for the short. A week ago I was brushing snow off the hood and a fat mouse came out of the cowl right above the blower motor. Probably the cause of the problem.

 

[choll]

I had the same problem with gen 1 light and everything. Spent many many hours with help from everyone here and still couldnt figure it out. Well while replacing my dash pad I checked all the wiring and I found that the fan motor switch, High-low, had a short. Replaced that switch and life is good.
Chuck

 

[Tanner]

Might also be a dying blower motor increasing load on circuit - mouse could have p*ssed in motor.

'Tanner'

 

[gglithox]

Fixed!! The wires going through the firewall and then to the blower had a spot worn from vibration. Wrapped good with electrical tape and now all is good. Thanks to all! Much appreciated!