A4ld 2 pin vs 3pin connector?

[Lets Play]

I'm in the middle of swapping transmissions and near the neutral plug (round) there is a 2 wire plug. On one of the trans it is a 2 pin and the other it is a 3 pin.
The truck is a 1986 BII 4x4 and the donor is a 92 explorer 4.0 4x4What is this pin/plug for and since the truck only has 2 wires and the trans has 3 prong plug what is the most common fix?
Thanks

 

[TwoWhels]

2 pin your computer only controls lock-up torque converter

3 pin also controls 3-4 gear shift

quick cheap fix

get 3 pin plug,
one wire power all time
other 2 ground to energize solenoids
you can use your computer for lock-up converter
use switch to manually engage 3-4 shift

 

[TwoWhels]

little more work

swap 2 pin valve body, 2 pin plug.
think your going to have to swap internal shift linkage anyway

 

[Lets Play]

Thanks but I think I have a bigger problem. I didn't fully understand the whole picture for replacing the trans and didn't seat the torque converter in the trans and probably screwed the torque converter or pump up.
So I'm probably looking for another auto trans.
Lesson learned