If my grid heaters are running, while the blower motor is running it will blow a fuse what is causing this?this will only happen @ an idle when i first start it up.

 

That's a good one, does this happen on all blower speeds? What is the voltage showing on the gauge when this happens? Is the correct fuse installed? If it's doing it on high blower speed perhaps the voltage is dropping off too far and the amperage draw from the motor is blowing the fuse. I would check the ground from the fan motor, if it's not tight it will cause this. Could also be the fan motor is on the way out.

 

Load test on fan motor , should pull just under what the fuse ratting is .
Info on truck , yr mod ect ?

 

truck is a 2002 2500 . it only does it when the volt gauge is reading low after the wait to start goes off.