87 4.0L Manual Upshift Indicator wiring at 4 pin ecu/trans connector

[MancheKid86]

4wd ax15/np231 swapped from  2wd ba10/5

As i am repinning the 4 pin connector for reverse lights (melted connector)
noticed the red/black wire to ecu and black/blue wire b5 in firewall junction. which in the fsm electrical confirms upshift circuit
+when probed upshift light comes on.


iirc the upshift indicator is preprogrammed to come on at a specific rpm range of engine
does it connect to anything or is it just used as a diagonstic port to ensure function of the factory set up shift indicator?

 

[eaglescout526]

It connects to a sensor that I dont think can be had new anymore. The sensor has a sprung ball bearing on the end of it that pushes against a shaft in the transmission that sends the speed back to the ECU to trigger the light.