In Need of Info - GP Relay

[my19997.3]

Sorry, this will be a long post:

I bought a new relay hoping this would correct the issue I have been having with the rough starts. Friday, Dad and I were looking at some info provided to me in another thread regarding the testing of the relay and the GP. Here's what we did:

Key off, I had 12v on the booted side of the relay. Dead (no juice) on the other side. (of course this is the large studs on the relay and not the small ones. According to the info I was provided for testing, I then had Dad turn the key on to fire the gp up and test the relay again. I had 12v on the booted side and , zip, nada on the other side again! TF?! Does this mean I have been starting the truck without any help from the gp? Then Dad was explaining the way a relay works. He said I need to find out what makes the relay close. Where does the feed come in to tell it to close for 30 - 120 secs. Please help .......

[vitalidle]

The red wire and orange wire or the small post wires are trigger wires. One is from the ignition and one is from the pcm.

[my19997.3]

Originally Posted by vitalidle

The red wire and orange wire or the small post wires are trigger wires. One is from the ignition and one is from the pcm.

Is there a way to test any voltage on the small studs? How can I tell if the relay is getting a signal to close?

[vitalidle]

When you cycle the key to the wait to start you should have power to those small posts for up to 120 seconds. Thats all dependent on if the engine is cold on how much time the pcm keeps the glow plug relay activated. Cycle the key and if you have power to the two small posts your relay is bad if you don't have 12 volts going to the gp's. Or you could use jumper wires from the battery to the two small posts and see if you get 12 volts to the gp's.

[my19997.3]

Originally Posted by vitalidle

When you cycle the key to the wait to start you should have power to those small posts for up to 120 seconds. Thats all dependent on if the engine is cold on how much time the pcm keeps the glow plug relay activated. Cycle the key and if you have power to the two small posts your relay is bad if you don't have 12 volts going to the gp's. Or you could use jumper wires from the battery to the two small posts and see if you get 12 volts to the gp's.

That's what we thought . When I had the tester (digital Fluke tester, Dad's a Master Electrician) we did not have any juice on either small post. We placed the neg off the battery post and tested the pos on the small studs. IS there a different way I should test them? What should I look for next?

[vitalidle]

Go to the local auto parts store and buy two jumper wires with aligator clips. They are handy to have in the tool box. Clamp each wire to the two small posts and the pos side of the battery and see if you have 12 volts out to the gp's. If you don't then check your wireing back through to the pcm. You might have wiring issues or a bad pcm possibly. Does the wait to start light come on in the truck?

[my19997.3]

The Wait To Start light does come on and I hear a "drumming" sound coming from the pass side under the hood.

[vitalidle]

Okay well thats what I would do you can either buy the jumpers or make your own. That will let you know for sure if the relay is bad. Hopefully its the relay. If not start checking the wiring next

[my19997.3]

Are there any type of fuses I should be looking for? According to the Haynes book I have, it said something about the GP banks are protected by a fuse for each bank. According to the GP troubleshooting, the banks have a fuse for each but it doesn't say where they are located. I wasn't sure if they were located on top of the motor somewhere in a harness.

[vitalidle]

No you need to find out if you relay is bad so if you have 12 volts to the battery side of the large post you need 12 volts going out the other large post side so what you need to figure out is if your relay is bad or the trigger wires aren't working. By the sounds of it your trigger wires are not energizing. If you have the wait to start light in the cab the pcm has power. So by using the jumper wires you are taking the trigger wires out of the equation and supplying a known 12 volts to the small posts to see if you relay will then have 12 volts going to the opposite large post not wired to the battery. You will hear it click if it works