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Wiring Check for AW4 Brake sense and tcu/pcm


NAXJA Forum User
Hoping someone that knows more than me can chime in and let me know if I'm going about this correctly. I'm swapping in a 95 XJ 4.0/AW4 into a 85 CJ7 with a Dana 300 tc. All the wiring is complete except for the brake light switch for the AW4. When I started this swap I pulled the engine side wiring from the XJ (pdc/pcm) and the trans controller. Unfortunately, I did not pull the brake light switch or harness from the donor truck.

Looking at the diagrams it looks like the brake light switch controls the transmission lock up through a (-) ground signal. No brake and the circuit is grounded, when you apply the brake, the ground is cut (ie no ground). Am I reading this correct?

Next it looks like the brake light switch also has a "speed control brake switch output". What does this control? Is this something that the PCM or TCU needs or is this for cruise control or another aux feature?

Lastly, I tested the wires for the brake light switch to the PCM and TCU. They both look like they originate from a rounded rectangle 12 pin connector with a white face. If I use my existing CJ harness to run the brake lights, can I just switch this wire so it is grounded when the brakes are NOT applied and break the circuit when the brake pedal is depressed?

Any help would be greatly appreciated as this project had stalled for 2 years but I'm 90% done and itching to get it on the road.