The problem I have with glow plugs on a 6.5 .I have a 1999 Grumman Olsen with a workhorse or GMC running gear. the engine is 6.5 diesel automatic trans. I just bought this van from a company that keep them mechanically sound so don't think any patch work has been done on truck.Problem, I found that the glow plug light in dash was not coming on so i checked and there was no fuse in fuse panel for glow plug, it goes on Eng 1 so i put in fuse and turned on switch and everything worked as planned, went to start vehicle next day and when i turned on the switch to the run side for glow plugs to preheat started engaged and would not stop until switch was turned off. tried a few more times same thing so i re moved the glow plug fuse and everything was back to normal other than hard to start due to cold weather. I have unplug ignition switch and a few other things trying to figure out what was wrong, then put fuse back in and it blew fuse i put in another fuse and worked as suppose to then next day tried to start and same problem, Do i have a wiring issue , could the ignition switch be the cause or what. I know that i have something that is feeding power to the starter are there any sensors that could cause this or is it maybe the glow plug wire and starter wire are coming into contact,dose anyone have a source for wiring schematics showing the glow plug wires and starter wires so i can trace them, I was told this was the same as most 3500 model trucks or van thanks for any help or leads on fixing this

 

I'd guess that there's a short in the GP circuit and it's backfeedig through ground to the starter

 

Go to your local NAPA store tell them to give you a push button switch I had the part number but cant find it but it only engages when depressed and wire it up between the 2 terminals on the GP relay and your problem will be solved

 

Sounds like the starter solenoid S terminal feed wire is shorted to power from the glow relay signal wire or a glow plug wire.

Can happen easy with all the heat from exhaust manifolds in that area-look for wires in the loom that have melted together.

Did the starter stop turning when the glow cycle ended?
Did it begin again when the afterglow happened?

 

dont no did not wait the time for it to cycle turned switch of ,is the cycle about 8 to 10 seconds or longer, I have also said it could be the ignition switch to or even ground wires not grounded properly. would like to find wire diagram so i could see wire route and colors. Thanks for your help

 

The ignition switch could be involved,it is a multi contact switch and contacts fail separately,grounds are an unlikely cause though.

The power flow is from the fuse to ignition through a safety switch(clutch/neutral safety switch) and on to the starter,it is + the whole way through.

 

update on problem, i have found maybe part of the problem, i have found a sensor or sending unit that is located on the back of head on passenger side, it has two wires to it i unplugged it and everything worked ok glow plugs starter work correctly. checked the wires and one side has 12 volts with switch on in run other side has nothing,,plug it back up and problem comes back. can someone tell what this is could this sensor or sending unit be bad and how can i check it, took my tester and what ever this is i can tough it with tester and beep goes off so i now no that the prong make a circuit.

 

Sensor on the back of head is normally used on mechanical injection engines for glow plug temp activation.
Not sure why a 99 would have it but the grummen vans are an animal all their own.

 

i unplugged it and everything worked fine i think,,so plugged it back and problem can back so i unplugged it everything worked fine so once engine started i let it run for a while and then stopped engine and plugged it back and everything worked fine so this has something to do with problem and engine cold, I also notices that temp hand appeared to move even after engine ran for 45 min or so and outside temp here was around 65 or so.Can someone tell me how this could feed back to starter and also how to test this sensor or sending unit

 

I think you still have 2 or more wires melted together in the wire loom somewhere.