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Wiring Harness Differences
In my on going saga of trying to get rid of the Glow Plug Control Module and Wastegate codes, I discovered something today.
Tracing the 1086 circuit from the PCM #101 pin to the #13 pin on the 42 pin connector I have zero resistance (a good thing). However from the #13 pin on the 42 pin connector to the #8 pin on the Glow Plug Module connector I didn't have any connectivity. After removing the wiring harness thinking I had a short I discovered a discrepancy in the schematic print outs for the GPCM. One schematic said to check continuity from the #8 GPCM lead to the #41 pin at the 42 pin connector, while the other said the #13 pin. UGH! My thinking is that when a previous owner replaced the engine with a 2002 model, they left the 2002 harness on the motor. I cannot verify this unless I have the correct schematics for both the 2000 and the 2002 California version glow plug modules. Has anyone run into similar issues? |
Not all 2000 trucks had GPCMs. My California truck doesn't, and never came with one.
My truck did, however, come with cab lights, as well as an overhead trip computer / compass / temperature / fuel economy meter, as it is a Lariat. Nevertheless, it did not come with lighted vanity mirrors, despite being a Lariat. When I picked up a pair of lighted vanity mirrors in 2001, I found that I needed to replace the entire A Pillar harness, as there was no wiring in the original harness to accommodate the lighted visors. So apparently Ford does not give away free copper. Wiring harnesses are often assumed to be all the same, but in my experience they do appear to differ, depending on the presence or lack of equipment, even if the bulk of the harness is the same, down to each connector. I have found "missing" wires in GM harnesses as well, even when I assumed it would have been more production efficient for GM to include the same harness in all similar models for manufacturing simplicity. But no, instead, the wires that aren't needed simply aren't there, even though the connectors are the same. I've had to add those wires after the fact, in cases where I wanted to add optional equipment after the fact. |
Chassis wiring harness have many variables according to how the vehicle is spec’ed out but I would be surprised to find the injector and Glow Plug pin outs vary by year. Pretty sure they keep the same pins throughout the years. |
Thanks for the replies.
I know my glow plugs are working because my truck starts quite easily even int 15 degree temperatures. However the leads not matching on the circuits is totally puzzling. All the troubleshooting guides say to check continuity on the 1086 circuit from the #101 pin on the PCM connector to the #8 Pin on the green GPCM connector. This is what brought the discovery that my 42 pin connector on the female side (top) doesn't match the pin locations on the 42 pin connector male side. I went a head and switched the wire locations just to see what would happen. The continuity check on the 1086 circuit is now complete but the glow plugs are not operating since the truck won't start when cold. This leads me to the conclusion (may be totally off base here) that the PCM control wire is actually pin #9 on the GPCM and the common wire is pin #8 which is the reverse of what I read on the schematics and have been told to check by professionals. I am going to switch the wires back to their original location on the female side of the 42 pin connector so I can start and drive the truck again. It was running just fine but I cannot get rid of the glow plug and waste gate error codes. Going to take someone a lot smarter and more experienced than me to figure this one out. |
Switch the wires back to the former locations as stated in above post. Truck fired right up. Of course codes came back on second start up telling me the glow plugs aren't working when I know for certain they are.
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Just curious how you know for sure the glow plugs are working correctly ? |
I have been chasing these codes ever since I bought this truck.
Put new glow plugs, new control module and then checked UVCHs and for operation via voltage check and cold weather starting. The truck will start in 15 degree temperatures with one cycle of the glow plugs. This is the third time I have traced these circuits because I cannot get rid of the codes. They go away when cleared but come right back. On this check I found the discrepancy at the 42 pin connector as outlined above. I had contacted Dieseltech about the PCM and sent him pictures of mine. He was a bit puzzled by my PCM internals as it seems it is an older version PCM but has the right programming for my truck. He suggested I check again for a short in the circuit and so here I am. |
Have you physically removed the engine wiring harness, stripped the tape and plastic split loom off and visually inspected each wire 100% ? I had a mechanic who insisted that he ohm’ed the harness and swore it was ok. I pulled it and found 2 wire breaks. Point being don’t take it for granted....dig in and inspect, the harness is easy to remove. the weak link in the wiring harness is where the plastic split loom ends to allow a new branch of wires, it is not uncommon to find wire breaks at or near these joints. It typically happens when somebody pulls the turbo without removing the wire harness. They end up resting the weight of the turbo on the harness while they are wrestling it out of its home. The other failure point is pulling the pins loose from the connector shell either at the Glow Plug Module or the valve cover. |
If you do unwrap your harness make sure to use the correct products to rebuild it. tesa makes the best harness tape IMO, I use the 51036, high abrasion resistance and temp rating. It doesn’t turn into goo when it diesel touches it like black tape. eBay or amazon is a good place to find it. https://www.tesa.com/en/files/downlo...-solutions.pdf https://www.ebay.com/itm/4-Rolls-of-...72.m2749.l2649 also make sure you get the high temp Nylon split loom as the polypropylene stuff falls apart in an engine compartments heat. this is a decent bundle of the sizes you will need. https://www.ebay.com/itm/1-8-1-4-3-8...72.m2749.l2649 |
The old harness is typically brittle from heat cycles so I redo the whole engine harness. You will need the 1” size to do a complete rebuild. https://www.ebay.com/itm/Nylon-Split...72.m2749.l2649 |
Thanks for the links. I did take the entire harness out to check it. That's what brought my attention to the the pins not matching up.
https://cimg4.ibsrv.net/gimg/www.for...ebeab8d8de.jpg |
Fwiw..... looked up the 1086 circuit in my 2001 factory wiring manual. it shows from PCM pin 101 to pin 13 at c138 ( 42 pin connector) and then to pin 8 at the GPCM From 101 to 13 and 13 to 8 you should have some resistance since in fact a current flowing through wire creates resistance. your. If you have no resistance that points to a broken wire. |
Where or what manual did you find the discrepancy in pin outs ?
i think the 101-13-8 pins are correct and whatever manual you found saying otherwise is wrong. if it was a ford factory manual please provide the manual number and page number and I will look it up online. |
1 Attachment(s)
Okay, here is one that shows the 1086 circuit going from #8 on GPCM through the #14 pin on c138 to #101 on PCM
(Sorry it's so small) https://cimg0.ibsrv.net/gimg/www.for...b21416af78.jpg Yet the connector says circuit 1086 is on the #13 pin https://cimg3.ibsrv.net/gimg/www.for...b4cfe8dc53.jpg Attached is a .pdf file that shows the 1086 going through the #13 pin to the PCM #101 |
Looks like your first pic might be from a technical bulliten ?
without knowing the source I would disregard the info... the second pic is taken directly from the 2000 factory service manual. I’d go with that. |
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