Yesterday went out to start the truck and it wouldn't start. First thing I did was jump the two big posts on the glow plug relay. It started right up! I changed it for new relay. This morning the truck did the same thing and wouldn't fire. I jumped the posts and it fired up again? It's a '95. Any other ideas as to what it could be? Thanks!

 

Does the Wait to Start light illuminate?
Check #22 fuse under the hood.

Be sure you are getting power to the gpr when the ignition switch is first turned on.

 

sounds like the signal side of your relay isn't getting the juice it needs. since it will start when you jump the terminlas you are get battery power to the large post on the relay but the ground fromt he computer or the constant power to the other small terminal isn't doing it thing. I would pull the two small wires back off and check one for power witht he key on and turn the key off. hook a test light to to battery power then the other side to the second small wire then turn the key on. the test light should light as the computer grounds this wire. then the wiring needs to be checked. if the wiring checks out it could have a bad PCM. I have seen the driver for the glowplugs go out before on a superduty and it didn't affect anything else in the PCM. if you have no ground you have 2 choices, new PCM or install a momentary switch to activate the glow plugs manually.

 

Thanks for the responses! I'll start doing some checking as soon as I get home later. Thanks.
Gregg