Engine Bay Wiring Identification

[Maxwellvis]

Anybody have any ideas as to what these two plugs are for?
Previous owner tore engine out 27 years ago and didn't label anything.
Normal engine wiring is figured out, but these two plugs are where I'm stumped.

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The yellow goes from the 2 pin plug straight to the 4 pin, the pink/black goes into the 4 pin from the main harness and has a second pink/black that runs to the other side of the 2 pin.
Maybe weird quadrabog wiring for the 4 pin and choke light/oil switch stuff for the 2 pin?

 

[Maxwellvis]

The other wiring that I've kinda got an idea about but am unsure of is these red and blue wires.
They're paired up together starting on the wheel tub and run back towards the trailer hitch. But don't have any plug or label on them, just bundled back there.

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Assuming something for a 7 pin harness possibly? (Truck has rpo UY7 - HD 7-LEAD TRAIL. WIRING)
The big relay beside the little junction turns on with the key and off when you switch to cranking.

This is an '84 GMC K2500 Suburban by the way, forgot to mention.

 

[edgephoto]

The red and blue wires are added on by a previous owner.

The 2 pin connector looks like an alternator connector. The other connector I am not sure of. Get us an overview shot of the engine compartments we can see where that connector is located in the harness. Also, if you download the wiring diagram and look for those color wires you might find it that way.

 

[edgephoto]

Poking through the wiring diagram I think it is a connector for the Speed SW Relay. I think it has something to do with cruise control but I am not sure.

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[75gmck25]

My ‘75 camper special has a relay in about the same location, and it’s for the camper wiring and 2nd battery. For my truck it is activated by an ignition-on wire from the fuse box, and was designed to provide isolation of the aux battery to power the camper when the engine is not running.. I’m not sure what type of function it would have for the trailering package.

 

[Jgonick]

Found same diagram as @edgephoto

Looks like it dealt with the TRC system it once had. Based on looking at diag- The white wire coming from tach off distr is going to speed switch then from switch it signals the valve- That is my guess.. see other attachment-

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[Maxwellvis]

The red and blue wires are added on by a previous owner.

The 2 pin connector looks like an alternator connector. The other connector I am not sure of. Get us an overview shot of the engine compartments we can see where that connector is located in the harness. Also, if you download the wiring diagram and look for those color wires you might find it that way.

My only opposition to the red and blue being PO added is that it’s got a factory looking tag near the hitch at the rear, naturally, it’s not legible at all.
I’ll see about grabbing a photo today if the rain lets up some.
Im kinda thinking it goes along with @75gmck25 ‘s idea for the second battery this truck used to have, assuming for pull behind camper setup perhaps?

Thank you both @edgephoto and @Jgonick for the identification of these plugs.
Sounds like they’re getting tucked out of the way, as I have none of that equipment and it probably wouldn’t be going back anyway…

 

[Jgonick]

My guess is heavy duty trailer & aux battery- i agree with @75gmck25

look at attachments- notice the fuse on red line for trailer and also has a blue wire for aux, (blue wire doesn't look quite correct -but I still think that is what it is)- and the setup for aux battery looks correct. Camper equipped- pretty much the same setup

 

[edgephoto]

I wonder if the red and blue wires are a GM accessory?

 

[Steelbuddha]

Here's the installation manual for the Painless 27-circuit GM truck replacement harness. Everything is identified by color, which can help a lot. https://painlessperformance.com/wp-content/uploads/2024/02/90627.pdf