Mystery wires near fuel sender

[magicpotato]

This is on a 91 Syncro. Found some unplugged wires near the fuel sending unit right behind the charcoal canister. Colors are BR/BK and BR. It has a specifically shaped plastic connector. I can't figure out where this is supposed to go. The fuel sender unit has the same shaped male connector, but it is already occupied with another set of wires. Swapping these two results in the fuel gauge not working. The BR/BK wires is hot when the ignition is on. From the Bentley manual, the wires should be from the digifant ecu, pins 13 and 19. Stumped on this one. Any clues or suggestions would be greatly appreciated!

Van runs ok with these disconnected, but I'm experiencing Vanagon syndrome at high RPMs, though I think it's unrelated.

[MarkWard]

The Syncro’s were wired for a rear decoupler and a front locker. The harness for the rear decoupler was stashed near the sender. My hunch is if you jump it, the center light will illuminate on the locker switch panel.
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[magicpotato]

That makes sense. My van has a rear locker, but it was disconnected at some point. A project for another day

[Howesight]

My 1986 Syncro came from the factory with the rear diff locker. I added a front diff locker and a de-coupler which is when I fished our the hidden wiring harness connectors that are installed in all diff-lock equipped Syncros.

I can confirm that the shape of the connector in the OP's picture is the shape of all three of the pre-wired connectors.
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'86 Syncro Westy SVX

[4Gears4Tires]

I have just been wondering this the last weekend while I sorted my fuel pump wiring out. I'll tape it up and ignore it.
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'87 Syncro
Ferric Oxyhydroxide Superleggera Edition