Glow Plug Wiring - Left side / Right side different?

[jmiller]

So we had some rubbing of a glow plug wire that eventually caused a short
to the frame on one of the glow plugs. This severely damaged the glow plug wiring harness.


I can't quite understand why the left side and right side of the glow plug
harness are so different and don't seem to match the wiring diagram in the
service manual or general guideline for fusable link sizing in a wiring harness?


So in looking at the wiring diagram in the manual and the glow plug harness, I be
became concerned with differences. The wiring diagram shows each bank on separate
14 gauge fusable links and 10 gauge wire to each glow plug and a 18 gauge fusable link for each glow plug.

The wiring harness has major differences between the left and right bank.
The left bank glow plug has a 14 gauge fusable link. Two 12 gauge wires to each pair of
cylinders 1-3 and 5-7. Then 18 gauge fusable links to each glow plug.


The right bank has the 14 gauge fusable link, like the left side. Then the 18 gauge
fusable links for each cylinder connected to separate 16 or 18 gauge wires to each glow plug.

Other than the right side wires having Teflon insulation for heat.

Why are the right side wires to the glow plugs such a small in gauge???
Was it because Teflon wire is very expensive??? (like a couple dollars per foot, that much more for larger gauges?)

BTW, the repair of the damaged harness followed the manual, the #2 cylinder now
has a 10 gauge wire between the fusable link and the weather pack connector.
In reality, I could have used 14 gauge instead, but I had the 10 gauge wire handy.


As a note, the general guide line for fusable links is two wire sizes smaller
than the main circuit.




Worn spot: (from #2 cylinder)

Caused: (Melted insulation and a burn out in the main harness, not the fusable link)

Right side of the Glow Plug Harness (replacing the fusable link)

Left side of the Glow Plug Harness

 

[Brooklyn Tow]

Ever figure out what was going on?


Thanks,

 

[jmiller]

That was the easy part, a direct short to the frame after the insulation wore through caused the burnt wire.

The wire rubbing on the frame was inattention on my part after head gasket replacement.

I had problems figuring out why GM built a harness that could burn up like that!!!

The wire gauge is too small on the right side for the fusable link being used.

 

[jmiller]

Again: it's all fusible link - just get the same color and yer good to go - that orange stuff on the turbo-side ends is silvered-wire teflon-insulated, not easily damaged, and can be crimped to new fusible link wiring, just like oem - fusible link is fine-strand silicone-insulated wiring for high heat areas, color-coordinated to actual size in mm - try to burn it with a hot soldering iron - rest of the engine harness is coarse-strand silicone-insulated wiring - try to burn it with a hot soldering iron................

Multi-strand fusible link is used for the glow harness because it will endure higher internal heat than the normal engine bay harness wiring, particularly as the gp's oft have a tendency to direct short - the link wiring can melt without destroying the insulation and adjacent wiring in the harness - can also endure higher external heat without damaging the wire conductors - ideal for gp systems harness - match the color for the correct size, or clean the insulation and note the wire size as printed thereon

So if the glow plug harness is all fusible link, then why did this wire melt the insulation the length of the run,
exposing the wire? (fusible link insulation is not supposed to melt!!)

Note the heat shrink and the section of blue 0.8mm^2 fusible link that I broke disassembling the harness.

I don't understand. With an 20 yr electrical / electronics background, and formal auto / diesel training,
I just don't f'n understand! :mad2::mad2:

Please help me understand!!!
Because my knowledge says, this wire that melted is not fusible link. I also tells me that this
16 ga / 18 ga wire is under sized for the fusible link in series with it. This tels me that the right side
of the glow harness is under sized between the glow plug that the fusible link.

 

[gmctd]

Can't really say, other than that wiring has been in harm's way for a long while - mine certainly doesn't look like that, nor, I betcha, does Turbine Doc's, or Chris's, or Rigger's, or many others here and there - that's more in the class of a fluke, and I ain't talkin' yer hi-bucks 8 1/2digit DVM, here - however, let me clarify: off the glow controller is fusible-link, then that large orange wiring to each side is standard silicone-insulated elevated-temp engine bay wiring, then that gray\blue wiring is hi-temp silicone-insulated fusible-link - on the turbo-side that smaller orange wiring, stiffer than the rest, is teflon-insulated vht wiring - as you can see, the insulation is correlated to the max area temperature - however, see if you can even brown any of that insulation with a hot soldering iron - it's all better than 450* rated - btw, hitcher local boneyard, see if you can find a suitable replacement - prolly better luck finding a 6.2 glow harness in good shape

 

[Missy Good Wench]

The glow plug harness comes from the factory all tucked up nice and neat with clips, shields and all sorts of protection.

The 6.2 engines were relatively easy to keep the wiring out if harms way. Now the 6.5 TD is another story.
The LH side is easy but the RH side takes care and attention to detail to be sure that the clips, shields and other goodies are kept in good order.

The routing of the glow plug wires on the RH side is tedious at best.
The front and rear plugs are relatively safe from heat damage as long as one pays attention to how the wire is routed.
The two center ones have the special High heat pigtails that go down the heat shield tubes.
The harness comes through by the starter and then swings out to a clamp at the frame rail and then splits into one lead that goes forward to the # 2 plug and the two for # 4-6

The center ones of late have ceramic plugs to help with the heat issue.

The heat shields are a must have item though and I have seen these left off. (Bad Plan)

If you route the wires correctly and make sure all the clamps are in place and wires are secure so they cant touch hot or sharp stuff they will do fine.

Had the wiring been run behind the engine and across the firewall and around the inner fender so that the aproach was from the side it would have been sweet.

Unfortunately this plan requires a lot more wire and the engine is wired completely before the body goes on at the factory. The units are all plugged in after the body is set on.

Just reapir as needed and secure everything well.

MGW

 

[TurboTahoe]

My own harness on the Tahoe was clearly 'hacked', probably because of the 3" lift.

1) What gauge fusible link should I use?
2) Where do you get the special ceramic plugs?

Thanks,

Rob