Chrysler Repair: cruise control: 99 TJ, vacuum servo, momentary switches

Question
QUESTION: I have just installed a factory cruise on 99TJ, but it does not even turn on.
The TJ was factory pre-wired, so i just replaced the clockspring, added the switches, vacuum servo.... everything according to the factory specs, but i can not make the cruise working. It does not even turn on (the green cruise lamp).

I did tripple check all wires, checked all voltages, brake switch, steering wheel switches... everything seems to be OK. At the end i did new wires, measured everything... I have also tryed to simulate the "cruise on" conditions to the PCM using resistors (the steering wheel switches are "resistive logic" ) - also without any result.

When i try to test the vacuum servo using DRB scan tool - everything works fine, PCM responds, the servo acts as it should. The same is for the cruise lamp in dashboard.

It seems to me that my PCM does not recognize the cruise On/Off switch,
Is it possible, taht my PCM does not have a software for cruise in it?

I also tryed to flash the PCM with newest software for my M.Y. - also without any result.

ANSWER: Hi Pavel.
I am impressed with your knowledge of the system. I don't have any wiring diagrams spedific to the Jeep TJ line, but the other Chrysler cruise systems use a straight through (no resistance) connection between sensor ground (vehicle ground) and speed control switch siganl (pin 41) to turn it 'on'. Have you checked the continuity of that connection? On the PCM, why not check the part no. of yours against the parts manual listing at a dealer parts counter?
Good luck on the project.
Roland

---------- FOLLOW-UP ----------

QUESTION: Thank you for your answer.
I have all wiring diagrams and FSM from TJ Wrangler. Cruise control uses 5 momentary switches on the steering wheel - each of the switches has its own resistor built in and all of them are wired together to 2 wires which go through clockspring directly to the PCM. So when pressing any of the switches, there is a different resistance between these two wires, so there is a different voltage drop for each switch. This is known as "resistive multiplexing"
The crusise switch sense is then between pin 32 of the 3-rd connector of the PCM and sensor ground.
For on/off switch there should be 900 ohms, for canncel 0 ohms (shorted) etc.
I have even tryed to simulate these valuse directly on the PCM plug - no result.

My PCM part No. matches the dealers one. There are only few P/N s for my modell year and there is no difference except of the emissions , country, fuel and transmission type.
There should be no difference in equipment level as the PCM should "recognize" the add-ons through its sense inputs. (as it does with A/C)

Answer
Hi Pavel,
There appear to be several iterations of the resistive logic (as shown in Chrysler car/van manuals in that time frame) as to on/off and set requests so I can't speak authoritatively of what should be the case for your TJ model. I would only suggest that you verify that the control switches you have are consistent with the wiring diagrams for your specific model. It may be you are not getting the 'on' or the 'set' function because of a mis-match between the what the pcm is looking for and what your switches are putting through in terms of continuity/ground/resistance measurements.
Also be aware that the servo requires continuity from pin 5 of the pcm (a separate on/off switch)
that is located on brake stop lamp switch, and that switch has to be patent when your foor is 'off' the brake. Were that switch not making good contact it would disable the cruise system (as if you had your foot 'on' the brake). It may be that your brake pedal return spring is weak for example.
Roland