Brake Signal / TCC Ground, and Park Neutral Signal into PCM.

[paradigm]

The black/white stripe is the ground & the orange/black stripe is "hot"/signal feed. As for the circuit numbers, I have a collection of electrial manuals for '78-'88 & get them from the diagrams or in some the list of circuit numbers & names. This makes things easier for cross checking changes in harnesses & components.

According to this diagram, it looks like the park neutral switch provides ground to the factory computer, so I should be taking the ground off the orange / black wire? However when I connected it to the LS PCM, it didn't seem to make much of a difference in idle speed going from Park or Neutral into Drive or Reverse.

 

[64nailhead]

I think you’re somewhat confused. I wish I knew what the ECM needed for each condition, but I’m not a factory ECM guy.

I’m confident that your ECM has two inputs. The question is whether they are 0 volt or 12 volt. 0 (zero) volt implies that ECM is looking for ground when the brakes are applied. This means that whatever switch you use (NOT the factory G body brake light switch with the orange wire). You need to use a normally closed switch (like the G body TCC switch) with one side to the ECM and the other side to a ground. So when the brake pedal is not depressed ( the button on the switch is pushed in by the brake pedal) the circuit is ‘open’. As soon as you push the pedal, the switch makes continuity, and the ground is applied to ECM wire - which in turns activates that input.

Sounds extremely confusing, I know I was confused when I 1st messed with this. Do you know how to check the brake switch (in your photo) with a multimeter? Testing with the switch not installed will tell if you the switch is normally open or normally
Closed.

 

[paradigm]

I think you’re somewhat confused. I wish I knew what the ECM needed for each condition, but I’m not a factory ECM guy.

I’m confident that your ECM has two inputs. The question is whether they are 0 volt or 12 volt. 0 (zero) volt implies that ECM is looking for ground when the brakes are applied. This means that whatever switch you use (NOT the factory G body brake light switch with the orange wire). You need to use a normally closed switch (like the G body TCC switch) with one side to the ECM and the other side to a ground. So when the brake pedal is not depressed ( the button on the switch is pushed in by the brake pedal) the circuit is ‘open’. As soon as you push the pedal, the switch makes continuity, and the ground is applied to ECM wire - which in turns activates that input.

Sounds extremely confusing, I know I was confused when I 1st messed with this. Do you know how to check the brake switch (in your photo) with a multimeter? Testing with the switch not installed will tell if you the switch is normally open or normally
Closed.

The LS PCM is looking for ground when the brakes are applied to control the torque convertor lockup. I got ground off the TCC / brake switch. However I am not sure how the LS PCM has been wired to the 700R4 trans to control it, as the transmission is mechanical.

The next issue I have is sending ground to the PCM for the park neutral signal to tell the PCM to use the appropriate timing tables when the car is in park / neutral. I took the signal off the orange/black wire going to the park neutral switch on the steering column, however the return ground (black/white stripe wire) from that switch was likely disconnected when the factory ECM was pulled, so I will need to ground the black/white stripe ground wire.