I have read all the glow plug posts in the forum and still have have not been able undrstand my problem, please help if you have any info. My 1990 F250 7.3L- Will not start unless plugged in (then it starts immediately) I have had glow plug/relay problems in years past so the first thing I checked is the voltage to the glow plugs, and there was none so I figured it was the relay like last time (2 years ago) and replaced it- still no juice to glow plugs or to the other side of the relay, then I figured it must be the controller, replaced that, still no juice to glow plugs or the other side of the relay. Then in the process of tinkering, I noticed that when the double brown wire (that sends juice to the glow plugs) is disconnected from the relay, now I do get juice to the other side of the relay but as soon as I touch the double brown to it's terminal on the relay, the meter shows no juice at the plug side of the relay. Then with the double brown still attached, I unplugged all the glow plugs idividually and then it did again show current at the plug side of the relay, but when ever I plugged any one of the glow plugs back in, the meter then showed no current at the plug side of the relay. This problem has surrpassed my knowledge of the glow plug system. The glow plugs (motorcraft) were replaced along with the relay, not last winter but the winter before. Thanks for responding...

 

GP's
Hi,
I posted the same response to a few other posts on gp problems:get rid of all that wiring and put in a manual gp switch, it's worked for me and in the worst cold conditions.

I had all kinds of problem too, no juice to the plugs, sometimes they came on while driving and burnt out,one bank would work and the other wouldn't. The manual switch is the best solution, go here for the diagram:
http://www.members.shaw.ca/k2pilot/

Magic