Yes, they are being marked wrong, That's mass production for ya!

Or you have excessive resistance between GP side of the relay and glow plugs.

And just to be sure, you do have the green wire on the glow plug side of the Z resistor, the Yellow wire on the Relay side of the Z resistor.

-Enjoy
fh : )_~

 

Yes, the small green wire from the controller is attached to the GP end of the Z bar and the small yellow wire from the controller is now connected to the relay end of the Z bar. When I started working on it the yellow wire was connected to the large power-in stud of the relay along with the double yellow power-in wires but I saw in the photos in the GP Sticky thread that this was wrong. Some "Non-Master Electrician" worked on this truck previously. There are numerous burned out fusible links and melted wires in the electrical system.
Did connecting the small yellow wire to the power-in side of the relay burn out the controller?

More information: I disconnected the Z bar from the relay and connected my VOM to the end of the Z bar and to the engine block. The meter only reads .6 Ohms, basically the value of one glow plug. I admit that the VOM is a freebie from China via Harbor Freight but shouldn't the VOM measure the total resistance of the Z bar, the wiring and the GP's?

 

I'm a bit fuzzy today, I hope this is clear ...

No, I do not believe the yellow wire misplacement will damage the GPC.
The Yellow and Green wires are Reference wires.

Resistance testing the system like that is pointless! It will not test it's capability to carry a load.

That's what you need to do, is test it under load. ie drop test.

Hook it all up as it should be. Ensure all Glow Plugs are connected.

Ensure you have solid ground from battery to motor ... Motor to GPC.

Ensure all power draw is off, Everything off ...

Test your battery voltage and take note of it at the battery posts!
If it's not over 12v+, charge the batteries.

Then ...
Remove the white wire from the small relay terminal.
Set your VOM for 12v+
Connect the Positive (Red) lead of your VOM to the Positive Battery Post, Not the terminals or any other place, to the Battery Post.
Connect the Negative (Black) lead of your VOM to a Glow Plug Terminal without unplugging the Glow Plug, just slip it up enough to hook up. (It MUST NOT touch the wire connector, only the glow plug terminal or it will not test that connection)
Connect one end of a jumper wire to the small terminal on the relay where the white wire was, Hold the other end safe from ground ...
Turn key on (add ignition power to relay, small terminal opposite of where the white wire was, ie Red Ignition wire).

Now, touch the Jumper wire to ground for no more than 10 seconds ... Take note of the voltage.

It should be between 3-5v+, Any more than 5v+ you have an issue in the wiring.
Technically it should be battery voltage minus 9v. If your battery is 12.5v, it should be 12.5-9=3.5v+.

The system is designed to bleed 3 to 4 volts, The Glow Plugs are only 10.5v.

You can do this to each GP, they should all be the same, if you get a higher voltage on a GP then the rest, that GP has a connection issue between the GP and the GP harness.
Be sure to let them cool for a bit between Glow Plugs.

Hopefully that's clear ... If not say so, I'll try and clear it up.

Never short the white wire itself to ground while there is power to the GPC, it can possibly damage the GPC.

-Enjoy
fh : )_~

 

OK, I just did this test.
Starting the test the batteries show 12.6 volts.
Upon connecting the jumper wire (in place of the GPC white wire) to ground the voltage immediately drops to 5v then 4v then 3v about 1 second apart. After dropping to 3v it continues to drop slowly to 2.3 or 2.4v at 10 seconds when I disconnected the jumper. All 8 GP's react the same way: 5-4-3 rapidly then slowly to 2.3 at 10 seconds.
What is this telling me?

 

that they are working properly. the hotter the glow plug gets, the higher the resistance, the less voltage drawn.

 

Then it is safe to say my controller is bad?
After completing the test I reconnected it and the relay clicks off and on rapidly.

 

that would be my assumption if all the other connections are good.
when you jumper the ground for 10 seconds, did the truck start?

 

I didn't try to start it. At this point I'm just trying to get the GPs working.

 

That your Relay, Glow Plugs and Harness are working just fine ...

Ensure your controller is wired correctly, if it is, replace your controller or (choke cough gag) use a button!
Obviously if you want to use a button, hook one leg of the button to ground, the other to the relay were the white wire would normally be.

EDIT
There is no assumption ... If your GPC is wired correctly, then it is failed!

EDIT2
Do you have a WTS light hooked up? on the Blue wire from the controller?

-Enjoy
fh : )_~

 

No WTS light installed. I believe the GPC provides the Ground for the WTS- correct? In other words the light is "hot" whenever the key is ON and the GPC grounds it, illuminating it.

 

That is correct ... The GPC blue wire controls the ground for the WTS light.

I asked that because I was mistakenly thinking it would affect the GPC, It does not!
The GPC will work just fine with the blue wire unhooked ...

-Enjoy
fh : )_~

 

 

Yes, that's how mine is wired.

 

OK, I'm now on a mission to find a reasonably priced controller!
I noticed that it is very similar looking to electronic ignition (gas) control modules as in nothing but a 1" square computer chip embedded in a large heat sink with epoxy. I bet it doesn't cost $5 to make one.

 

Naw, They are more complicated then that ... Still pretty simple though.

Personally I would find a NOS unit or a salvage yard unit, I would not use an aftermarket version.

How about ...
http://www.ebay.com/itm/like/322113569458?lpid=82&chn=ps&ul_noapp=true
-Enjoy
fh : )_~