Vauxhall Vectra Cruise control problem

cruise controls are dependent on the following sensors all working together
brake sensor
clutch sensor
auto--vehicle speed sensor
rpm's sensor
fuse for the cruise control
cruise control switch either or all not working will stop the cruise control from engaging
road speed at which you can engage the cruise control has to be above a reset speed before it will cut in and work

not being informed if it is auto or manual, here are some of the items that control the cruise control
brake pedal sensor ,
clutch pedal sensor,
vehicle speed sensor
engine ignition control module , tacho ,
vehicle speed --will disconnect if the road speed is below setting minimum speed
ratio changing
bad cruise control switch
wiring and connections
ecm problems
problem cruise control module

Though I'm not familiar with the Diesel, most vehicles have two throttle cables. One is for the cruise and it's common for the plastic part at the end (throttle body) to break. This is the easiest fix, and very commonly the problem. Good Luck

The cruise control is normal disengaged by applying a little pressure to either the clutch or brake pedal. There are switches/sensors on the top of these pedals near the return springs. The retuns springs become weaker with time/use, so it is possible that they are not fully returning to allow disengage to reset so that it can be used again.
That is the cheapest fix and should be the first check.
The next is to cange the stalk as the switch at the end may be broken. Costwise it is relatively inexpensive for a replacement and to instal yourself. Make sure you've done the first part, or else you'll waste money and time.
Good luck.

the following items either individually or together stops the cruise control from working ( you didn't mention auto or manual box)
VSS, ( auto or drive shaft sensor in manual)
brake light switch / sensor/
clutch position sensor ( manual)
fuse
cruise control switch
,fuse
wire to the ignition control module /tacho
cruise control module
ECM

On these case,to troubleshoot these problem,there are solved help links.Click the link directly and refer the details to solve these problem yourself,with help of diagrams:------
Ford ranger cruise control not working?

http://technoanswers.blogspot.in/2012/02/ford-ranger-cruise-control-not-working.html

----------- Horn and Cruise control quit working?

http://howtobyme.blogspot.com/2011/11/horn-and-cruise-control-quit-working.html

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Horn and cruise control not working on Plymouth Grand Voyager?

http://howtobyme.blogspot.com/2011/11/horn-and-cruise-control-not-working-on.html

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Horn and Cruise control quit working on 2003 Jaguar S-Type? http://howtobyme.blogspot.com/2011/11/horn-and-cruise-control-quit-working-on.html

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Cruise Control stops working, Excessive cranks to start the engine and RPM goes max 2500 http://whoisbyme.blogspot.in/2012/07/cruise-control-stops-workingexcessive.html

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Cruise control stop working on 1994 Ford ranger? http://technoanswers.blogspot.in/2012/02/cruise-control-stop-working-on-1994.html

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Cruise control not working? http://schematicsdiagram.blogspot.com/2011/12/cruise-control-not-working.html

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1996 Ford Explorer: Cruise Control Wiring Diagram?

http://schematicsdiagram.blogspot.in/2012/06/1996-ford-explorer-cruise-control.html
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These will help.
Thanks.

check cruise control fuse

sounds like a switch not working right in the cruise control take it back to the guy who "fixed it" and get him to "fix it" right this time,, its likley to be the brake switch sticking on, this wont let the auto cruise control engage, it keeps thinking you are trying to brake to slow down so it kicks its self out just as it should if you were driving in auto cruise you then need to reset it to go back into auto cruise

take to auto sparky-sounds like solenoid

The cruise has no dedicated fuse, you will most likely be looking to replace the clockspring rotating contact located under the steering wheel which connects the switches in the steering wheel (horn, cruise and air-bag) to the rest of the electrical system.