Chevrolet Repair: cruise control, vacuum servo, cruise control module

Question
I have a gmc jimmy 4x4 4.3L, What i have done already was to test the cruise control switch on the column and confirmed that it is working I used a test light and checked the leads at the cruise control module when the buttons were pressed, so I changed out the cruise control module still nothing. Now when i get another chance to check the brake switch and see if it is sending a constant signal to the cruise control module if it is i will replace it and see if that fixes it or if not, what would be another issue to look for? the fuses are good. I very much thank you for you'r time on this matter. signed Ken

Answer
GOOD MORNING KEN, WELL YOU DID NOT TELL ME WHAT YEAR THIS IS,, BUT THERE IS NOT MUCH LEFT TO THE EACH OF THE SYSTEMS ANYWAY.[OLD OR NEW] IF THIS IS A OLDER GMC DID YOU CK AT THE VACUUM SERVO, THIS IS VERY COMMON PROBLEM, SUCH AS BAD VACUUM LINES BROKEN OR SPLIT OR NOT GETTING A VACUUM SOURCE TO THE SERVO BECAUSE THE PORT IN WHICH THE VACUUM LINE IS AT IS PLUGGED, SO CK THIS IF IT HAS A SERVO. SOME OLDER UNITS HAD A SERVO AND MODULE.  ALSO CK THE BRAKE LIGHT SWITCH FOR A SIGNAL AND THE VACUUM LINE ON SOME YEARS GOES TO THE SWITCH AS WELL..IF NEWER YOU ARE IN THE RIGHT AREA AGAIN,CK THE BRAKE LIGHT SWITCH. DID YOU REPLACE THE MODULE WITH A NEW ONE OR USED ??? I HAVE SEEN AFTER MARKET MODULES THAT ARE BAD OUT OF THE BOX. TO CONFIRM CK SIGNAL WHEN ENGAGING TO THE BLS,IF NOTHING I WOULD THINK WE HAVE A WIRE HARNESS PROBLEM OR MODULE PROBLEM. I AM NOT AT WORK TODAY,BUT IF YOU CAN NOT GET THIS GOING GET BACK TO ME ON THE YEAR AND WHEN I GET TO WORK I WILL LOOK THIS SYSTEM UP FOR YOU IN MY MANUAL.
LET ME KNOW,,, TOM...