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Discussion Starter #1 (Edited)
Hi. On my 1986 F250 6.9 AT, when I turn the key to crank/start, the glow plug light does not come on. (The glow plugs are NOT being energized, long crank to start).

I installed a new Glow Plug Controller and Glow Plug Relay, with no correction. I can hear the glow plug relay, "clicking" on and off, as if it it being cycled by a timer.

I have owned the truck for approx. 10 years and this is a sudden onset,new problem.

I have NO interest is converting to a manual (push button ) system. I have the 1985 Ford engine manual, but it only has a glow plug wiring diagram, no diagnostic "tree".

Thanks.
 

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Discussion Starter #2
Well, looks like the FSM shows 2 wires to the Glow Plug Controller should be hot w/ ignition on or start. red/litght green and pink / black. I'll have to check them tomorrow. Any other ideas, please chime in.
 

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Of what duration is the on / off cycling of the GPR? Is it short as in seconds or is it longer as in 2 to 3 minutes? i have read in another thread that if you have 2 or more bad glow plugs the system will cycle on / off like that in short duration cycles. Have you tested your glow plugs?
 

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Discussion Starter #4
Thanks for trying to help, YYC! I had no other participants, so I forgot the post the solution.

It turned out my old glow plug relay had failed. AND, the glow plug relay I bought from O'Rieley, (Standard Ignition RY175) is not wired correctly, internally. So it did not , at first, correct the problem.

I had to run a wire from the "I" terminal, on the relay, to ground, to make it operate as intended. I checked another (same brand, & part #) and it TOO, is designed incorrectly.
 
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