Glow Plug Relay Clarifications
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2nd Gear
Joined: Aug 2003
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Glow Plug Relay Clarifications
I've perused the other posts on glow plugs and still have some questions. I have an '01 F350 that's been getting pretty cold blooded lately. Have to cycle 2-3 times to get it to start on 10 degree days.
Last night I checked voltage across the two main lugs on the relay and showed 12v both with and without the key on. Normal or not normal?
Am I correct in understanding that I can test the relay by shorting the two main lugs together with pliers or something to see if the truck starts easier?
My relay has 4 wires. Two large and two small. What are the small ones?
Is the relay a warranty item under the 5/100,000 warranty or just the glow plugs?
Thanks.
Last night I checked voltage across the two main lugs on the relay and showed 12v both with and without the key on. Normal or not normal?
Am I correct in understanding that I can test the relay by shorting the two main lugs together with pliers or something to see if the truck starts easier?
My relay has 4 wires. Two large and two small. What are the small ones?
Is the relay a warranty item under the 5/100,000 warranty or just the glow plugs?
Thanks.
Senior User
Joined: Jun 2003
Posts: 400
Likes: 0
Call your local dealer and ask service. I don't see why not. AS FOR THE 2 SMALL WIRES. 1 is ground and 1 is power from ignition to activate the relay. Should only be 12 volts to 1 off the big or battery feed to the relay with the key off and a click and power on the other terminal with key on. I believe your issue is with GLOW PLUGS, there are 8 and only takes 3 bad ones to give you problems. Very easy to check. Good luck and let us know.
Senior User
Joined: Sep 2003
Posts: 369
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From: Brighton, Co
The glow plugs and relay are covered under the warranty. I wouldn't try shorting across the terminals as the glow plugs draw up to 200 amps then it gradually draws less until it gets to about 90 amps before the cycle is finished.
Senior User
Joined: Oct 2003
Posts: 101
Likes: 1
From: South Jordan Utah
Ohm out your glow plugs individually - some will have high resistance. My 95 F250 has shorted Glow Plug lines thru the valve cover gasket which burned up the glow plug relay. Shorder whrn the engine was warm I think.
Posting Guru
Joined: Nov 2000
Posts: 1,005
Likes: 1
From: Cincinnati, Ohio
With key off you should have battery voltage to one large terminal and nothing to the other large or either of the small terminals.
With key on for the first two minutes or so you should have battery voltage to both large and one small terminal. The other small terminal should show ground. This shows the relay active.
With the key on and after the glow plug cycle has finished you should have battery voltage to one large and both small terminals. The computer activates the relay by grounding the second small terminal thus activating the relay.
It is possible to have battery voltage to both large terminals when the relay is active and still have a bad relay. If the contacts inside are pitted or corroded you may have low amp voltage passing through it but not enough power to actually run the glow plugs.
I have an MS Word document saved with both instructions (complete with pictures) from a fellow member of another board (Carpentractor) and the originating thread of my post when I replaced the glow plugs on my truck a while back. It is specifically for the 94-97 trucks but the principles should be the same. If you would like a copy send me an eMail with the information you need and what site you saw this on and I will reply with an attachment.
Dave / Believer45
With key on for the first two minutes or so you should have battery voltage to both large and one small terminal. The other small terminal should show ground. This shows the relay active.
With the key on and after the glow plug cycle has finished you should have battery voltage to one large and both small terminals. The computer activates the relay by grounding the second small terminal thus activating the relay.
It is possible to have battery voltage to both large terminals when the relay is active and still have a bad relay. If the contacts inside are pitted or corroded you may have low amp voltage passing through it but not enough power to actually run the glow plugs.
I have an MS Word document saved with both instructions (complete with pictures) from a fellow member of another board (Carpentractor) and the originating thread of my post when I replaced the glow plugs on my truck a while back. It is specifically for the 94-97 trucks but the principles should be the same. If you would like a copy send me an eMail with the information you need and what site you saw this on and I will reply with an attachment.
Dave / Believer45
