I have a 1999 Gmc (workHorse) Step van with a 6.5 diesel engine when i put in the fuse for the glow plug and turn the switch to the run position the starter will engage, take the fuse out and everything works normal but hard to start.. there are other thingson this fuse acording to manual, heated O2 sensor, Seconday O2 sensor, mass air flow Sensor, Cam shaft Pos sensor, Evaporation Emission Canistor, Purge value soleniod. Fuel heater, Water in fuel sensor, Glow plug Control , Fan control relay and power breake booster fluid flow alarm. i have unplugged the wires from switch on the column and also a few other things and then plugged them back and everything worked ok then the next day tried to start and it did the same thing tried what i did first time and it did not work take fuse out and works ok put back in and happens again

 

You must have 2 wires melted together in the large harness along the back of the engine,starter/fuel heater,glowplugs?

 

Update on my finds, I have tested the fuse panel and have found that with ignition switch in run position i have power to one side of fuse 12 volts on ENG 1 in fuse box nothing on other side, this is with fuse out, i can turn ignition switch to start and i am getting 6 volts or so on the side that had no volts and still 12 on other, so this tells me that i am getting feed back from the starter solenoid i think. am I correct in thinking that there is one wire going to solenoid from switch that is grounded to something on fuse ENG1, The owners manual says that these things are on ENG1 Heated O2 Sensor,Secondary O2 Sensor,Mass Air Flow Sensor, Camshaft Postion Sensor.Evaporative Emmisin Canister,Purge Value Solenoid,Canister Vent Sensor, Fuel Heater, Glow Plug Control and fan control relay,. Can someone give me advise on which on of these are close to the starter wire . Picture of what each look like and there location would be great. As i said earlier with the fuse in the ENG 1 panel glow plugs work but starter engages in the run postion of ignition switch and even when engine starts that way starter stays engaged . Thanks for anyones help

 

Not sure if you even have 1 but the fuel heater is a good option,glow relay control is the other option from that list.

 

I have unplugged the plug with 3 or 4 wires on glow plug module and still have same problem looking at fuel heater next to see if this is the feed back cause