2000, 2500, Auto Transmission, 4WD
​​​​​​Everything is stock other than Airdog Fuel pump

Over the past 2 years gradually went from working sometimes, to never working, and then no dash light turning on when pressing button on steering wheel. Needing suggestions as I've already done the following in this order

1. New TPMS. Recently replaced due to super high idle at random times.
2. New vacuum tubing. Cruise control was intermittently working. Cruise light on dash would come on but would drop out of cruise on its own as if I pressed cancel or bumped the brakes so I thought perhaps it was losing pressure.
3. New cruise servo. Cruise still intermittent and wanted to rule out both any electrical or vacuum issues as it looked like the original part.
4. Verified that the cruise cable is functional as I've now replaced both the TPMS and the servo.
5. New steering wheel buttons. Was hoping this would fix the dash light, cruise control enabling issue as I'd already confirmed that I had voltage.
6. New clock spring. Horn always worked, airbag light still turns on and off like it should.. but still nothing happens when I press cruise button on steering wheel, figured might as well rule it out.
7. Checked all fuses. Nothing blown.
8. HVAC has always worked normally so don't think it can still be a vacuum issue.
9. No check engine light has ever popped up, checked for codes anyways. No codes
10. Replaced the brake switch even though never had issue with brake lights. Pulling up brake doesn't allow for cruise to turn on, so I'd think switch is good
11. No wire damage found in steering wheel, column or to servo.

I have 5 volts at the button wires.
Pressing on/off it goes to 1.5v
Pressing Set it changes to 3.8v
Pressing the buttons on the right side also changes the voltage readings, so I can assume that my buttons work.
I have good vacuum at servo, but no voltage. Since the on/off button doesn't turn on, this would make sense, right?

What have I missed?

 

ECM?

Kurt

 

It looks you've done some good troubleshooting already, and fired a fair number of shots from the parts cannon. If you don't already have one, get yourself a factory service manual (available on paper at Geno's Garage) or some other source for wiring diagrams and troubleshooting info. Using the wiring diagram(s), trace the wiring from the servo back to the source, which is likely the PCM. Can you back-probe the connectors at the PCM? The pics I see of them look rather odd, and I'm not sure if they can easily be backprobed - you might have to pierce wires instead. Do continuity and wiggle tests (preferably with the source connector disconnected). If you have a high-impedance multimeter (at least 1 mega-ohm, preferably higher - higher impedance = lower current draw = less risk of overloading internal PCM circuit), you can test for servo voltage at the source. I'm not familiar with the "logic testers" and such that are sold for automotive use, but they probably work too - the trick with any of these is that you'll probably need to back-probe the connector at the source. There are a couple of way to do that with a multimeter - it will probably be harder with the other types of testers. One way with the multimeter is male/male banana plug test leads with back-probing tips. The other is traditional probe-type leads with slip-on alligator clips and straight pins. There are piercing attachments too - just be sure to cover the tiny hole with liquid tape if you have to pierce.