It definitely sounds like the wire for the electrical kickdown switch. Power from the kickdown switch behind the accelerator pedal to the electrical kickdown solenoid on the transmission.
https://www.startekinfo.com/StarTek/outside/12253/program/ETM/126td83-85.pdf
Page 109 & 109/1
Also, note the difference between the 84 model vs the 85, which has the Compressor Cut-out Control Unit for the A/C. This may explain the slightly different routing of the wiring.