Engine cranks when connecting battery.

[mattsmoski]

1986 M1008, I have no more ideas on what is causing this problem.

One day the starter was having trouble turning the engine, kinda slow. Then it did start. The next day the starter would make no sound at all. Glow plugs cycle on and off. Both batteries are at 12 volts. I removed the starter and had it tested at an auto parts store and it would not turn or do anything. I replaced the starter with the correct Delco one. When I went to connect the battery back up it sparks too much, smokes a little and slowly turn the engine with the key out. I disconnected the ignition connection at the steering column, same thing. I checked the connections at the starter, they are correct and no shorts from the heat shield or anything touching. I disconnected the wire that goes in between the two batteries, when I began the starter removal. I replaced the Glow Plug relay. Because I thought that was malfunctioning because of repeat cycles of off and on. Any suggestions of what I can check. I have not done any modifications to this M1008. On the Glow plug relay there is two wires to the right and one on the left or top and bottom. One on top two at the bottom. Any advice would be appreciated.
Thank you. SSgt. Matt Smolinski, USAF, Ret.

 

[Evil Dr. Porkchop]

The starter relay under the dash could be stuck.
This thread explains the problem a little and shows where the relay is at.

doghead starter relay modifcation

*** WARNING LABEL *** Disconnect both batteries before attempting this procedure ____________________________ Credit goes to doghead for his instructions in thread "underdash starter relay" and the wiring picture as well. This modification replaces the standard GM underdash starter relay, GM...

www.steelsoldiers.com

 

[Mullaney]

1986 M1008, I have no more ideas on what is causing this problem.

One day the starter was having trouble turning the engine, kinda slow. Then it did start. The next day the starter would make no sound at all. Glow plugs cycle on and off. Both batteries are at 12 volts. I removed the starter and had it tested at an auto parts store and it would not turn or do anything. I replaced the starter with the correct Delco one. When I went to connect the battery back up it sparks too much, smokes a little and slowly turn the engine with the key out. I disconnected the ignition connection at the steering column, same thing. I checked the connections at the starter, they are correct and no shorts from the heat shield or anything touching. I disconnected the wire that goes in between the two batteries, when I began the starter removal. I replaced the Glow Plug relay. Because I thought that was malfunctioning because of repeat cycles of off and on. Any suggestions of what I can check. I have not done any modifications to this M1008. On the Glow plug relay there is two wires to the right and one on the left or top and bottom. One on top two at the bottom. Any advice would be appreciated.
Thank you. SSgt. Matt Smolinski, USAF, Ret.

.
I can't help but wonder if the truck managed to short circuit the starter wiring... Are you sure something didn't get up against the exhaust and melted off the insulation on the wires connected to the starter?