Refer To...

Marv and I are researching what it takes to add tap-up/down shifting to The Beast.

We could buy one of three nearly plug-and-play boxes, but they're all the same format and I don't care for how they did it.

In a word, cheaply.

Maybe $15 of components for $125 to $150.

I have the factory service manual and can see how the wiring for the shifter SHOULD run.

These shift box vendors have proven the BCM already has the programming to respond to the inputs once you run a wire between X1-17 and X1-20 on the BCM.

X1-20 shows a voltage drop from X1-17's 12v and that tells the BCM to ask the TCM to shift up or down.

What we've been trying to find is if X1-17 was hot all the time or just when the ignition is on.  We want the shift box we're making to open the switch when the ignition is off.  The factory shifter can't be in manual when you start the car because the switch can't be closed when the car is in Park or Neutral.  The aftermarket boxes are a simple switch you can forget in the 'on' position.  While nobody is reporting any problems, I don't like sending a "I'm in gear AND in park" signal to the, expensive to replace, BCM.

X1-17 also provides 12v to the cruise control switch which sends a voltage drop back to X1-3.

That sentence above took way longer to find than it should have because the table of contents and index don't include the words, "cruise control."

Happily, GM is a creature of habit and my other service manuals show that cruise control troubleshooting is at the beginning of section 9.  The Caprice, Impala SS, Custom Cruiser and Corvette manuals all have "cruise control" in their indices.

Grrrrrrrr.