PS1 dual analog flight stick mod for N64

I'm trying to mod a PS1 dual analog flight stick to use with the N64 and in particular Star Wars Racer.
However I'm not quite sure what to do with the potentiometers.
I was expecting to find 3 connections on both sides, but one side has 4. One should be Vcc, one ground and one data. No idea what the 4th is for. I traced it back to the only chip on the board, but I can't find anything on the chip's pinout...
This is the chip: SC405794DW C28W
It's a 28-pin SSOP.
One stick's 4th pin goes to pin 16 on the chip, the other to pin 18.
Any help would be appreciated... ^^

 

That 4th pin is just the data pin from the Y axis pot rerouted to the board of the X axis pot.
Probably to make the wiring tidier and give the sticks the slack they need to move around.
Should've just traced the other side first...

 

Finished...

 

Sweeeeeeet!!! That has got to be the best game choice ever to use with dual sticks!