No glow plug light, no start

[j7l2]

I am having a problem with my 6.5 TD. When I turn the ignition on the glow plug light does not come on and it won't start without the glow plugs. It is a 1995 Chevrolet 2500 ext cab, 4wd, auto, with 267000 miles. I replaced the glow plug module and it didn't change anything. Also checked the glow plug fuse and ign 1 fuse and both okay. Can this problem be caused by the PCM or the ignition switch or both? And how do I determine which one? Or is there something else that would cause this problem? I did get it to start once yesterday, after changing out glow plug module and checking the fuses with no success I came back out a few minutes later and the glow plug light came and truck started and ran last night. Today no light and no start.

Thanks in advance for any suggestions or comments.

Problem just started yesterday. About 2 weeks ago the PCM was replaced because of a different non related problem any chance of a bad replacement PCM?

Regards,
JimO

[racer55]

Do any of the other dash functions work when the glow light is out of order?
Like the fuel gauge,temp or any other normal actions?

[j7l2]

Everything else on the dash lights up and acts normal. I just need to know how to test that the ignition switch is good or bad and how to test the PCM to see if it is sending a signal to the glow plug relay.

Thanks for your comments.
Regards,
JimO