Ok we have had some cold mornings gets warm during day.but my indicator light in dash stays on for 2 seconds timed it its had tobstart glow plugs?relay? Both how much resistance should these glow plugs have when they are good. And its an 03 with the metal glow plug harness in it not saying the harnesses are bad but they are rusty. Anyone know the ok operating rang of these plugs or do you think bad relay?

 

The light is not an indication of how long the plugs are on, just that it's ok to start. If you have a gauge to watch main voltage, it stays on about 90-120 seconds and depending on temperature of the motor.

It was 40° here this morning, with the truck plugged in, the light never came on, I could see they were on by the output voltage of the alternator.

 

Here are my notes on glow plug stuff. They are cut and paste from other posts so don't read them like I'm giving instructions, I copied them to get the values and left the text so it would sort of make sense.

6.0 Glow plug wisdom

Disconnect the four-wire connector to the passenger side glow plug harness (the one with the red lock tab). Using your ohm meter (and the appropriate scale if it doesn't have the auto-range feature), connect the black lead to the passenger side negative battery cable and the red lead to each of the four cavities on the glow plug harness end. You should obtain readings between 0.5 to 2.0 ohms on all four circuits (cylinders #1, #3, #5 and #7).
-------------
Install an inductive ammeter on one bank at one of the two harnesses at the Glow Plug Controller Module (GPCM). You can get up to 200 A at first, but then should stabilize around 35-45 A. Check the other bank with the inductive ammeter. Both sides should read the same. If not, check the amps to each individual glow plug to determine which one (or ones) is bad. Each glow plug should draw 10-12 Amps.

Fuseable link for glow plugs about 4"" down the harness from where it connects to pass side battery. take the tape off. should be going under your a/c line.

All this information comes from the 2006 Service Manual.

Glow plug on time is dependent on oil temperature and altitude. The GPCM will
command the glow plugs on for 1 to 120 seconds. The GPCM does not operate
if the oil temperature is above 55C (131F)
It looks like the GPCM is really 2 units in one box.
Glow plug to ground 0.1~2 Ohms
Glow plug connector to GPCM connector Less that 5 Ohms

Pin #3 on both is the VBattery

Green connector
pin #1 is gp#5
pin #2 is gp#7
pin #6 is gp#1
pin #7 is gp#3
pin 8 goes to the PCM
pin 9 goes to the PCM

Black connector
pin #1 is gp#6
pin #2 is gp#8
pin #6 is gp#2
pin #7 is gp#4
pin 9 goes to the VPwr

The Glow Plug length of operation (up to 120 seconds) depends on oil temperature and the BARO reading. Glow plugs are not operated if the oil temperature is above 131 *F (55*C). The Glow Plug system is PCM controlled. The Wait-To-Start light is initiated by the PCM and is independent of the Glow Plug system. Above 131 *F, the PCM will still bulb-check the Wait-To_Start light. The GPM (GlowPlugMonitor) system (part of the OBDII system) is designed to monitor and detect failed glow plugs or failed wiring in the Glow Plug System.

https://www.ford-trucks.com/forums/1...ce-manual.html

Ford workshop diagnostic guide
https://www.ford-trucks.com/forums/1...ghtmare-9.html (post #135)

 

This also begs the question, does it do any good to wait to start for a few extra seconds? This would provide extra chamber heat correct?

 

I had to replace the Glow Plug Module on my 03 once so far, Hit 45 degrees and she won't fire. The routine that works for me, jump in, Key On, fasten seat belt, close door, Start truck

 

I also had some glow plug codes so I changed the ones noted in the codes to find out my module was actually the culprit.