I have a 1990 F350 7.3 with an ATS turbo that I've owned for about a year. About a month ago the glow plug relay began to chatter on cold starts and the WTS light would cycle about once per second. It was apparent the glow plugs were not cycling on. I replaced all 8 glow plugs with Motorcraft/Beru plugs with no change. I then checked the wiring harness and glow plug connectors for electrical continuity. I replaced all 8 connectors and repaired the damaged glow plug harness, there were 3 bad connectors and 2 bad splices in the harness. No change. I next replaced the glow plug relay, no difference. Next I replaced the glow plug controller and still no difference. The glow plug relay continues to cycle, the WTS light cycles about once per second, and the glow plugs are not receiving power to cycle on at cold start. What should I look at next??

 

I and many others will probably suggest it's what is on mine and it works nice is a push button for the glow plug relay mine is set so when you hold the button they are on

 

You may have a ground problem.

 

yup. i would check the grounds read good.
new relay and controller with new harness leaves only power into the unit. if you have 12volts in, the only thing left is grounds.

 

I tried a jumper from the glow plug controller ground at the base of the controller to the negative battery post, no difference. I checked voltage at the glow plug relay, 12.78 volts at the battery and 12.40 volts at the relay. Should'nt the voltage be the same? When I turn the ignition key on to check the glow plugs, the voltage at the relay varies all over from 8.5 to 12.8, voltage to the glow plugs is 0. Bad ground or bad wire feeding the relay? The wire harness feeding the relay has been spliced and wrapped in shrink wrap, the connection seems good.

 

You didn't do something like wrap the threads of your glow plugs in teflon tape or something like that which would prevent the glowplugs from getting a ground, did you?

 

I found my problem. The "seems good" connection feeding the glow plug relay is bad, I'll need to replace the wires. I also found the ground at the glow plug controller was not really very good. A combination of several bad electrical connections was the problem. Thanks to all for the help.

 

My wiring harness was toast and created more problems than it was worth. I bought a new one from Uhaul Truck parts. I think they still have some of these in stock. Works great!