What I did is rig a Anti Hi Jack system with a foot switch way up under near the E break. I have a relay under the console near the solenoid that breaks the black wire (GROUND) and locks the shifter in park. Me thinks you have a bad ground. If you have 12 Volts on one wire while stepping on the break pedal then it seems like you have a bad ground some where to activate the solenoid.

Just My $.02 worth...

 

Test the solenoid itself by applying 12v to it. Make sure you didn't get a defective new part. You could also load test the +12v and ground with a small 12v incandescent bulb to see if there is a damaged wire causing a voltage drop.

 

It seems like everything on the connector is in order in my opinion. Here is what I found with the PowerProbe:

A = no change in any way (key, brake applied, etc.”

B= 12v when brake is applied

C= ground

D= no pin

E= no pin

F= 12v constant

I connected the ground alligator clip to the ground on the shift interlock solenoid and applied power to the “B” terminal and the solenoid didn’t move would that lend credence to the part being bad?

 

Also..I just remembered.. There was an update on that harness. The plug with the wires coming out was replace with a new plug with Heavy Duty wires on the 2009.
I had a Failure or broken wire that cause the solenoid not to function. You had to splice the wires into the old harness. The failure was do to the fact that the harness moves back and forth when you move the shift lever.

In your case above it sounds like the Solenoid is toast. But I would check for bulletins on that connector and new wiring. Or check around just for that part. It is improved so as not to fail as the shifter moves back and forth

 

is GM 88967140 the part you have?

Going through you info:-

• Pin A - This should be connected to ground, you indicated "no change in any way" but not the actual voltage, would be worth checking.
• Pin B - Looks fine.
• Pin C - According to the diagrams this connects to Pin F(IGN) when in PARK providing +12V to the Ignition Lock Actuator. It might read as ground when not in park due to the low actuator coil resistance.
• Pin D - Fine
• Pin E - Comparing 04 to 08 diagrams now appears to be redundant.
• Pin F - Fine

To summarize, confirm that Pin A does connect to ground, with the plug unconnected check the continuity between B and A, it's hard to say for sure what the reading will be as GM sometimes fit electronics inside their components, however it might be just a plain coil so might read low ohms ( may be around 50ohms ish)

The other possibility it is solenoid being energized but is being mechanically restricted in some way.

 

So I did bench test with my PowerProbe on the old part and found something interesting.

This configuration works (retracts the white "holding" nub on the part when power is applied):
A - pos
B - pos
C- ground
D- not used
E- not used
F- pos

BUT! The configuration shown below also works.
A- ground
B- pos
C- ground
D- not used
E- not used
F- not used


So...any thoughts? I'm thinking I'll just rewire the "A" pin wire in the truck to a local ground under the center console. I'm more confused than when I started haha! I'll make sure to update this thread for whatever the fix is.

 

Seems like something strange going on, could you have a break in a wire that's confusing things?

Check out this post, see responses #14 and #19, perhaps as you move the connector an intermittent break in a wire "comes & goes" so to speak?

The only real way to tell is to continually measure the continuity through each wire directly to the plug pin whilst flexing the cable, the readings should not change i.e. very low ohms.

From your description, PIN A (GND) would be a good candidate, according to the wiring info below, the only pins of concern are A & B, pin E may be involved but not according to the 08 manual. 03-07-2023, 01:03 PM


Breaks in wires and bad switch contact are notoriously difficult to trace, this is where a multimeter needs to be relied upon, the slightest change in resistance can indicate a break

 

Much appreciated, oceanbrave! Just to be clear…those scenarios I mentioned were done while bench testing and trying different ways with a battery and PowerProbe; that’s not ground and voltage from the truck.

 

OK got it.

You side "rewire the "A" pin wire in the truck to a local ground" however according to both 04 and 08 wiring diagrams, pin "A" should already connected to ground (has to be)

The 04/08 wiring diagrams are incomplete regarding shift solenoid pin C, it looks like this ultimately connects to the "Ignition Lock Cylinder Control Solenoid" 2-pin connector wherever that is located.

 

My 2009 is wired the way Ocenabrave has shown in the 2008 diagram. By breaking the Chassis ground is how I got the anti Hi jack thang to work. Once you break that ground you have no solenoid operation. Again..my original fail was due to a broken wire in the moving harness which was updated by GM to a heaver gauge and thick insulation to prevent breakage from movement of the shift lever.