I have had a 2000 XJ for about 2 years. The previous owner installed the stock cruise control, but I realized that there is no way to disengage the throttle once you have engaged the cruise control on the highway. This and other things he has worked on lead me to believe he either did it wrong or it could be a bad actuator. I'm worried about safety so I need to get it fixed. Neither the brake, turning off the cruise, or turning the ignition off resets the cruise. My gut says it is mechanical and not electrical, but I need advice on what I should be checking. Is there a way to test the cruise control actuator or is there a way that he might have just hooked it up wrong?

Holy cow, This is serious. Even as familiar I am getting with these, this is one of those cases where liabilities are huge if anyone gets it wrong. I highly suggest you take this to a reputable shop and have this diagnosed and repaired. With this type of problem even I would fork out to have it personally looked at by someone else without a doubt.