I am having a problem with my glow plug system in that it will not always turn on when I turn the key. I had the module replaced about 3 years ago. So I am curious if there is anything I can do to fix it.

does the engine start?
could try ohming the glow plugs

After a few years the flat plug going into the GP controller gets a little wonky. Try cleaning up the contacts or better yet just replace the plug (about 10 bucks from GM). Also clean up all the engine and body grounds. Another problem area.

Bill

The engine will not start at all....it just cranks put never fires......the glow plugs are less than one month old.....I have power going into the relay but no power coming out.....think I am gonnna have to replace the relay module again....only bout $124 or so

if you dont have power coming out then the controller is not working or the relay is bad.
you could check to see that you are getting power on the control switching side of the relay, the smaller wires. Use a test lamp. If you are getting power there, then the relay is bad. You can just replace the relay. Otherwise the whole controller is probably bad. which is kind of odd that it went bad twice. But sometimes thats the way it is.

You can replace the glow plug controller with a parallel bank of horn relays actuated by a button in the cab. $1.50 per relay x8 = $12 plus some hook up wire and elbow grease. They're rated at 30A each. Been using those same bank of horn relays to control the glow plugs on my GM 6.2L for 3 years now. It also allows you to glow for longer periods in cold weather and afterglow. Also makes finding bad plugs very easy. Just check for ground at the N.O. relay contacts.

Just remember that you can burn out the glow plugs if you leave them on too long. They are six volt plugs running in a twelve volt system.

Those would be 9G 'fast glow' plugs, which have a tendency to burn out. To get around that issue, replace them all with self limiting 12V plugs. Either Bosch Duratherm or Delco 60G. You can hot wire them directly to a battery till the battery is flat without burning them out.

Thanks for all the help. I put a new relay on and it is working fine now.