I have a 99 ford f-250 and the glow plugs do not work, I have replaced both relays and removed one bank of glow plugs to inspect and according to Fords chart they look fine. When you try to start the truck the lights come on like they are suppose to and the lights dim like there is a power draw from the glow plugs but they seem to not work. If you leave the truck plugged in over night it fires up like you never had a problem, but I shouldn't have to do this unless the outside temp is low.

The only way to make sure your glow plugs are working fine is to use a multi meter and check for continuity,no continuity the glow plugs are fried.. ;)

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Originally Posted by harness4

I have a 99 ford f-250 and the glow plugs do not work, I have replaced both relays and removed one bank of glow plugs to inspect and according to Fords chart they look fine. When you try to start the truck the lights come on like they are suppose to and the lights dim like there is a power draw from the glow plugs but they seem to not work. If you leave the truck plugged in over night it fires up like you never had a problem, but I shouldn't have to do this unless the outside temp is low.

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Check the wiring harness between the glow plugs on each bank. I had the one on the right bank go bad, and it was not readily apparent from looking (broken wire inside the insulation) and so that bank was not heating at all.

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Originally Posted by harness4

I have a 99 ford f-250 and the glow plugs do not work, I have replaced both relays and removed one bank of glow plugs to inspect and according to Fords chart they look fine. When you try to start the truck the lights come on like they are suppose to and the lights dim like there is a power draw from the glow plugs but they seem to not work. If you leave the truck plugged in over night it fires up like you never had a problem, but I shouldn't have to do this unless the outside temp is low.

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My friend had this same issue with his 99 and it was a computer issue cost around 200 to fix at the ford dealer.

Take a test light and hook the alligater clip side to positive, yes, positive. Then ground the outside of the glow plug (maybe by the threads). Then, touch the probe end of the test light on the terminal of the glow plug. If it doesent light up, its bad. Also, check the wires toe the glow plugs, the glow plugs only come on for 5-10 seconds when you first turn the key. If this doesent work, please write back and let me know, I have many more suggestions.