You can get an aftermarket kick down cable for a 700R4. The adjustment is critical for the health of the transmission. The plug is for the torque converter lockup through the computer. There is an aftermarket kit available to engage the lockup without the computer. The pan has to be removed to install the conversion. Many just use the trans without the lockup.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine