annoying short
Thread Starter
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Mountain Pass
Joined: Jan 2008
Posts: 125
Likes: 0
annoying short
I have an 86 f250 6.9 that has a really bad short or ground problem.It does it the whole time the engine is running.If the lights are on they blink real bad[all of them and the glow plug light flickers on and off.the radio also comes on and off every few seconds if the truck is moving.I don't care much for wiring,so I can't say I've really traced it out but if anyone's had a similar problem I'd like to know. thanks.
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
The old style glow plug controller usually failed with the glow plugs turned on.
If that is what is happening , your glow plugs will be burnt out when you need them.
The glow plug load would also cause the lights to dim.
Look behing the passenger side battery and find this glow plug relay.
After you have the engine running, unplug the purple wire, marked controller in the picture.
If that stops the blinking, you need a new controller or convert to manual glow plug.
If that is what is happening , your glow plugs will be burnt out when you need them.
The glow plug load would also cause the lights to dim.
Look behing the passenger side battery and find this glow plug relay.
After you have the engine running, unplug the purple wire, marked controller in the picture.
If that stops the blinking, you need a new controller or convert to manual glow plug.
Thread Starter
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Mountain Pass
Joined: Jan 2008
Posts: 125
Likes: 0
Thanks Dave, but I've been seeing the glow plug diagram here and put my plugs on a manual switch just this week.They are working great thanks to you. The truck has been doing this for quite awhile.thanks
Junior User
Joined: Dec 2007
Posts: 82
Likes: 0
From: WA
Check all of your battery connections closely. I had an old VW that did this and I thought the stereo was bad. It would turn on and off as I drove down the road, turned out to be a loose positive battery cable. 
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
Notice the yellow wire at the bottom in my picture .
It used to be in the grey connector right below it with the green red wire.
The connector was melted on the yellow wire side, not making contact.
I cut the wire as close to the connector as I could on both sides.
Then I spliced it with a copper split bolt, then taped it up to prevent shorts.
After reading your post several times, the engine to chassis ground may be loose or bad.
Mine was from a manifold bolt to the fire wall in the wiper motor area.
You may want to check that as well.
It used to be in the grey connector right below it with the green red wire.
The connector was melted on the yellow wire side, not making contact.
I cut the wire as close to the connector as I could on both sides.
Then I spliced it with a copper split bolt, then taped it up to prevent shorts.
After reading your post several times, the engine to chassis ground may be loose or bad.
Mine was from a manifold bolt to the fire wall in the wiper motor area.
You may want to check that as well.
