Well, the dash connector was an issue, so replacing it was worthwhile, great that you solder, JJ_Jeep, these are resourceful skills that pay off! Sounds like a diagnostic check of the Air Bag system would be wise, for sure.
On the cruise control issue, you were at the "T" for the cruise unit. Check the reservoir vacuum seal from that same "T" to the bulb/reservoir at the front of the Jeep. A quick check for the entire system can be performed from the engine vacuum line that attaches at the intake manifold. Trace from the cruise to that elbow with the vacuum tube.
Hook up your vacuum gauge/pump there, and pump down vacuum. The entire system should hold vacuum. If not, the leak is somewhere between the intake manifold and the reservoir. Possible bleed-offs or leaks from that circuit would be the heater and A/C vent controls, the cruise vacuum circuit, the one-way check valve for this vacuum circuit and the reservoir bulb itself.
If you're curious about the trouble areas for the cruise control, this is the "factory" approach to a defective speed control system:
If a road test verifies a system problem and the speedometer operates properly, check for:
- A Diagnostic Trouble Code (DTC) If a DTC exists, conduct tests per the Powertrain Diagnostic Procedures MDS2.
- A misadjusted brake (stop) lamp switch. This could also cause an intermittent problem.
- Loose, damaged or corroded electrical connections at the servo. Corrosion should be removed from electrical terminals and a light coating of Mopar MultiPurpose Grease, or equivalent, applied.
- Leaking vacuum reservoir.
- Loose or leaking vacuum hoses or connections.
- Defective one-way vacuum check valve.
- Secure attachment of both ends of the speed control servo cable.
- Smooth operation of throttle linkage and throttle body air valve.
- Failed speed control servo. Do the servo vacuum test.
As you know, I like to start with the easiest prospects first before parts replacing! Check for a vacuum leak, either tubing or the reservoir bulb itself, each can be confirmed with your nifty new vacuum pump tester. Check out the brake light switch function and the switch point for the brake lamp switch. Make sure you do have electrical current, try to find that fuse circuit, and if you can't find it readily, let me know, I'll provide information.
I can also provide more information on each of the systems mentioned. A vacuum check at the cruise servo can confirm the "one-way check valve" function as well as the speed control servo condition. Check vacuum at the "T" near the cruise servo in all three directions:
1) Cruise servo (only) direction as you did.
2) Check the combined servo and check valve*, using the "T" end facing the reservoir.
3) Check the "T" end to the reservoir to isolate and test the reservoir tube and reservoir bulb only.
4) If the reservoir feed line leaks down, isolate the reservoir itself and vacuum test it.
*The check valve is an inexpensive item. This trouble spot traps the manifold-to-reservoir air in the system and prevents vacuum fluctuation. It is a simple one-way valve located between the manifold and the first junction of the cruise and heater-A/C vacuum circuit. The check valve helps stabilize vacuum, otherwise manifold vacuum fluctuates widely. Visualize the vacuum "trapped" between the reservoir and check valve, with the recharge of vacuum coming from the manifold source.
Let's look for a simple fix before parts replacing, JJ. From my article, you can see how a split in the vacuum tube from the reservoir to the cruise "T" was enough to keep the XJ Cherokee's cruise and vents from working when the engine was under throttle. A defective check valve would have a similar effect.