99 7.3 Glow plugs won't work

[Bentspoke]

I have a 166K mile 1999 7.3 F350 that I've had the relay changed on and now it still won't start below 45° without being plugged in. I checked he plug that goes in the passenger side valve cover and it was tight and in good condition so I'm at a loss on this one.

Do I need new glow plugs or might there be an electrical problem that's keeping them from working? Is there a way to check?

Any help would be great! Thanks

[SuperCrutyPS]

Is your glow plug relay working? It may looking like a starter solenoid that is near the front of the engine on the passenger side of the valley near the valve cover.

You can check to see if you have voltage into it and out of it while the WTS light is on. If no voltage out, the glow plugs won't heat.

[rich00dually]

+1 for the relay. common problem, cheap easy fix