2005 Grand Cherokee cruise control works intermittently

The cruise control on my 05 grand cherokee has been starting to act up. If i turn it on before the engine has warmed up, it will turn off immediately, but if i let it warm up and I get going a steady speed going down the highway, then turn it on. It might work. I believe the problem is related to the vacuum system, but I'm not a car expert and not sure where to start looking into this problem? does anybody know where i can get a diagram of the vacuum system? or any other ideas you might have regarding the cruise control?

I do not know if your 05 is like my 97, but under the brake pedal there is a little switch that activates the brake lights and turns off OD, this is known to go bad. I would check this first, if it is bad then your brake lights will stay on when your OD disengages. If this is the problem you can do like me and super glue a couple of pennies to the back of the peddle for a quick fix.

Is your problem fixed?