So I bought a 96 powerstroke a while back and the guy said it had fairly new glow plugs in it. They worked fine up untill it got real cold. It just wouldnt start. The light stays on the right amount of time but they are obviusly not working. If I plug it in for a while then it will start. Do you guys think it could be the relay? I know that if there is one shorting out the light goes out quickly. SO I don't think this is the issue. I would greatly apprieciate any help you guys might be able to give.
Thanks

 

Without the pulling the GPs to verify they're "fairly new", I'd suggest testing the GPRs. Also check the condition of the connectors. If they're melted or burned, you may problems with UVCs.

 

Test the GPR with a test light. see if each larger lug has voltage with the key on. use a friend so you don't have to quick run to the relay to test. If you have voltage on both its good and you need to test the Glow plugs. If you don't have voltage on both lugs with the key on the relay clicks on then you need a relay.