Need an Engine Wire Harness

[Kwing]

The wiring harness for the engine on my 2007 Tahoe 5.3 is toast. I'm inclined to just replace the whole thing rather than **** around with repairing or rebuilding.

Problem is I can't find one.

GM part number is 25809100, but is discontinued and nowhere to be found.

Are the any sources for a new harness, even if it's just some kind of aftermarket LS swap harness? Or a good source for used harnesses?

 

[SpareParts]

Pull a part, wrecking yard, marketplace surly some are being parted out.

 

[Kwing]

Pull a part, wrecking yard, marketplace surly some are being parted out.

So far, on eBay, I am finding roughly the same playing field as what's available new... up to '06 only, or for the 6.2 only. There are small number of what look like the right ones, but none of them have a matching cross reference number, and all of them have various chunks of the harness, or at least a handful of connectors, cut off of them. For $300 and up, that doesn't sit well.

Pull-a-Part is a crapshoot even if they do have the Gen 3 chassis on the lot. While they never have before, it's been about a year since I tried, so I guess it's worth looking again, crapshoot or not.

I haven't tried marketplace, but I will tonight.

I'd much prefer new, even if I gotta splice some connectors on here and there. Some splicing on an otherwise new harness is a million times better than any used, unknown condition rats' nest... which is basically what I already have, LOL.

Thanks for the suggestions!

 

[Fless]

Look on www.car-part.com for pre-owned harnesses, if you're so inclined. They might be more intact. Or not.

 

[Kwing]

Look on www.car-part.com for pre-owned harnesses, if you're so inclined. They might be more intact. Or not.

It just keeps kicking back a "non-interchange search result", which looks like an error, but I can't be sure because it's about as clear as mud. Doesn't seem to like 2007 or 2008 search criteria.

 

[Fless]

Here's some search criteria that I used with mucho results (obviously use your ZIP):

Either one of these two selections returned many listings:

 

[Kwing]

If I had another half a brain, I'd still only have half a brain, LOL. Thank you!

I'll have to make some calls from those results in the morning.

Side note, I'm getting a lot more search results for new harnesses searching specifically for LMG 5.3L harness instead of by Tahoe or with 25809100 number, but all of them state 2009 and up LMG, not '07 (or '08).

Anyone know what makes an '09 different from an '07 if all the specs seem to read correctly?

 

[Joseph Garcia]

If I had another half a brain, I'd still only have half a brain, LOL. Thank you!

I'll have to make some calls from those results in the morning.

Side note, I'm getting a lot more search results for new harnesses searching specifically for LMG 5.3L harness instead of by Tahoe or with 25809100 number, but all of them state 2009 and up LMG, not '07 (or '08).

Anyone know what makes an '09 different from an '07 if all the specs seem to read correctly?

There were some mid-series for the GMT900's, and U think that they were made starting in the 09 model year. @Doubeleive may be able to be more specific for you.

 

[Kwing]

Thanks for all the help!

And big thanks to @Fless!

Got one from a salvage yard on the other side of town. They said it's had the two rear O2 connectors cut off, but that is one part of my existing harness I know is intact, so I'll take it. Other than that, they said the condition is "great". We'll know for sure when I hobble down there this afternoon.

It was an eye-watering $385, but my time and sanity is worth more than that... or so I'll continue telling myself, LOL.

Thanks again!

 

[Doubeleive]

Thanks for all the help!

And big thanks to @Fless!

Got one from a salvage yard on the other side of town. They said it's had the two rear O2 connectors cut off, but that is one part of my existing harness I know is intact, so I'll take it. Other than that, they said the condition is "great". We'll know for sure when I hobble down there this afternoon.

It was an eye-watering $385, but my time and sanity is worth more than that... or so I'll continue telling myself, LOL.

Thanks again!

have fun there is a reason that wire harness cost that much, easier to remove than it is to install, install involves a lot more work
I would label everything as you remove the old one and then label the replacement identical
if a connector has no connection label those as well NC, that way your not sitting there wondering where did that one go.....

 

[Kwing]

have fun there is a reason that wire harness cost that much, easier to remove than it is to install, install involves a lot more work
I would label everything as you remove the old one and then label the replacement identical
if a connector has no connection label those as well NC, that way your not sitting there wondering where did that one go.....

Yup.

The tears have now started to flow, LOL.

The "new" harness has the 18 wires that go to the MAF, AC limit switches, and through to the firewall just cut off. "Great", I think, "I can just slap an 8-pin and a 12-pin Deutsch on there and connect new to old", i tell myself...

Ha effing ha.

Among the 18 wires, although the same 18 colors exist on both sides, each side has FOUR pink wires, 3 tan-ish wires, 2 purple, and 2 black/white wires, all identical shades and gauges.

I have no clue which of the same color wires should go to each other, and the schematics in the Haynes manual are useless without knowing what every circuit is. Can't find anything online either .

Anyone have any expertise or advise to climb THIS hurdle?

 

[Kwing]

I'm in the "home stretch" of this bite i shouldn't have tried to chew. These 18 wires are the last WTF I got ahead of me (unless I eff something else up before the finish line).

Anyone have a feel for how risky it might be to wire nut the unknowns together and fire it up to see if anything's wonky?

 

[SpareParts]

Should work fine.
Beware though. There is nothing more permanent than a temporary repair that works.

 

[Kwing]

Should work fine.
Beware though. There is nothing more permanent than a temporary repair that works.

Well, the wire nuts are just to be able to swap them around if something doesn't work. Once everything is working, I'll crimp the pins on and feed them.into the housing(s) with the rest.

I just don't want to cook something... else.

I THINK the black/whites are both grounds, which I think should be fine if they get swapped, and I have roughly 70% confidence the tans are too, but the purples and pinks scare the snot out of me, because from the little bit of the circuits I do know are in this bundle, the pinks appear to be signals, and I have no clue about the purples...

 

[mikez71]

So 18 wires that go through firewall? Is that ALL the wires that go through firewall?
Or just the 18 that have duplicates?

You can meter the connector ends to find out where they go?

charm.li has wiring digrams.

Also look for 2007_LD_ElectricalUtilitiesSUV.pdf here somewhere
https://www.gmupfitter.com/light-duty-vehicles/light-duty-prior-to-2013/

I don't think wire nuts are risky, but guessing on 10 wires...

 

[Kwing]

So 18 wires that go through firewall? Is that ALL the wires that go through firewall?
Maybe pictures would help..

You're gonna have to meter the connector ends to find out where they go.

charm.li has wiring digrams.

Also look for 2007_LD_ElectricalUtilitiesSUV.pdf here somewhere
https://www.gmupfitter.com/light-duty-vehicles/light-duty-prior-to-2013/

I don't think wire nuts are risky, but guessing on 10 wires...

Fair enough, LOL.

I get a D- for effort, but I had to tap out for the night. Just gonna have to resume in the morning. Still got a lot of parts to put back on...

Here's the branch coming off the harness, branching off just before the passenger side ignition and injector section:

And here's the vehicle side. The MAF pigtail branches out of this bundle, as does the AC limit switch and another 3-pin connector that looks like whatever it goes to is wrapped around the negative battery cable, the rest of it goes through the firewall:

I'll check out that link and see what they have. I was also thinking of trying to call the dealership in the morning to see if they have a 25809100 specific schematic. Not getting my hopes up, but worth a shot, right?

 

[mikez71]

Enoug fun for tonight, get some rest!

I bet once you separate the known wires, if will be much less daunting. One color at a time.

Were those two ends connected? Do you mean the wire bundle ran along the firewall, not through it?
If they were connected, you might grab a magnifying glass and see which ends mate up..

I'm guessing mostly ECM stuff.
O2 sensor have a couple pink wires.. Black/white maybe grounds on front passenger side of engine.

 

[Kwing]

Enoug fun for tonight, get some rest!

I bet once you separate the known wires, if will be much less daunting. One color at a time.

Were those two ends connected? Do you mean the wire bundle ran along the firewall, not through it?
If they were connected, you might grab a magnifying glass and see which ends mate up..

I'm guessing mostly ECM stuff.
O2 sensor have a couple pink wires.. Black/white maybe grounds on front passenger side of engine.

I wish it were that simple... on all accounts, LOL.

Those two ends were not connected. The harness shown on the ground is the "new" harness I got from a salvage yard on Friday. They told me it just had the 2 rear O2 sensors cut off of it, but made no mention of these 18. Unfortunately, in my arrogance and lack of forethought, I cut the original harness off of that bundle and subsequently trimmed and stripped the vehicle side wires, so I can't match the cuts up on the original either.

As far as the branch running along the firewall, with the O2 sensors and such on it, that's the branch before the one in question (moving from the ECU toward the passenger side). That one is now fully intact after splicing on my original harness' O2 connectors.

On the vehicle side bundle, I can identify 10 of the 18 easily enough: the 5 for the MAF, the 3 running to whatever is around the negative cable, and the 2 running to the AC low limit switch. The other 8 run down in a single loom along the AC suction line and look like they go through the firewall with the suction line, but I guess it's possible they don't and I just can't see where they route from there. But yeah, have no clue what those 8 go to.

And on the harness side, even with the 10 I can identify on the vehicle side, I have no clue which pins on the ECO connectors correspond to them.

 

[Kwing]

Also look for 2007_LD_ElectricalUtilitiesSUV.pdf here somewhere
https://www.gmupfitter.com/light-duty-vehicles/light-duty-prior-to-2013/

Those are the first pinouts I've seen for the ECU connectors on this truck. Thank you!

With those pinouts, process of elimination using what I do know throught the harness and the 10 i can ID on the vehicle side, I bet this will get me to what the remaining 8 are for and which sets go together to connect the 18.

I greatly appreciate the help!

 

[mikez71]

another e38 ecm pinout with some specs from 'verlon' found here...

E38 Complete Pinout

Here is a E38 complete pinout. Information is gained by pieces from GM SI, tracing and probing disassembled ECM PCB and reverse engineering of several OSes. 129235

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