I have a wire that is loose that I am reasonably certain goes to the GPR. Based upon the attached photo (courtesy of Guzzle7pt3.com), it is the wire that is labeled "Purple Wire" which is attached to the large terminal that feeds the both banks of GP's. The loose wire appears to be more of a blue than purple on this truck and is actually crimped/soldered/connected/heat shrinked to a wire that is white with a light green trace once it goes into the wiring loom which is shared by the Brown/Yellow wires.

I removed the nut that would normally hold the ring terminal connector to the post; however, there is no remaining portion of a broken ring terminal to provide a further clue.

The below, very simpified, wiring diagram does not show this "purple" wire unless I am misreading it.

So, my guess is that the PO just shoved some copper wire under the nut and tightened it down and it has finally come loose, probably while I was replacing up pipes, pedestal, and turbo.

I am not doubting that the information contained in the photo is correct: however, does any one know where this purple wire leads to, terminates, or what it powers?

So far it seems as though the glow plugs, both banks, are operating properly with the wire disconnected based upon VBatt+ alone.

 

IIRC, it's a monitor wire. I think it only monitors during a KOER glow plug test, though. I'm going off memory here; I'd have to look at the manual to be sure.

 

Yes. It lets the PCM know that the glow plug relay did what it was commanded to do for diagnostic purposes.

 

Many thanks to both of you.

I found a diagram to the pins to the PCM about 5 minutes ago and it corresponds to pin #8, circuit 1277 which is the "glow plug relay monitor".

 

Does the PCM monitor the voltage on this "purple" wire referenced in the photo above (PCM Pin #8, Circuit 1277) on every start cycle? Or just during diagnostics tests commanded by a scantool, as Pikachu suggested?

JHL3... the purplish blue part of the wire is actually a fusible link. That's why it has all that dual layer shrink wrap for the splice. If the outer layer of that heatshrink says "SCT" and a number, like "SCT 3", then that leaves little doubt that it was a factory splice, not something that the previous owner did, even though the glow plug relay in the photo is an aftermarket, not a factory relay.

SCT heat shrink was made by Raychem, an aerospace and defense contract supplier formerly known as Radiation Chemistry. They invented heat shrink, and whenever I see SCT heat shrink on Ford products I know that at least in that one narrowly defined area, Ford didn't cut corners.

Further up the harness, beyond the purple blue fusible link, the wire you are asking about turns to White with a Light Green stripe, which goes through the 42 pin connector and eventually lands at Pin 8 in the PCM, defined as Circuit 1277.

Ford describes this wire as monitoring the "left bank", but as you can see, it isn't possible for this wire, on the relay style in the photo, to distinguish the voltage between banks. Some interim California emissions trucks, built before the solid state Glow Plug Control Module, had a different style relay with a bare bar bridge over the output terminal, that separated left and right banks. In describing the simpler Federal 49 state relays, Ford may carryover terms and designations that aren't really applicable.

E-Series Econolines use a White with Violet Stripe wire for the same purpose, only it goes to Pin 9 of the PCM, as Circuit 1278. It may have also been for the "Right Bank" on PCMs where each bank was monitored separately, on Califorina trucks with the relay that had the bus bar bridge on the output terminal.

There is yet a third circuit, 1279, which is a White wire with NO stripe, that goes to Pin 34 of the PCM. I'm not sure what that does, or what applications utilize it.

The GP control wire from the PCM is out of Pin 101, and is a Violet with Orange Stripe wire. I want to say Circuit 1085, but my focus in looking into this has been more on the voltage monitoring that the glow plugs see, not the on/off control by the PCM.

 

It would be nice to have the glow plug relay monitored all the time but is only checked during the diagnostic routines. A lot of time and frustration for beginners would be saved on no-start diagnosis if there were constant, real-time moitoring.

 

Sorry, wrong thread.