I've got another stupid one. Well not so much stupid as I never got it working right.
Don't laugh: I tried to stick cruise control on my 1.6 Astra. I was doing a lot of miles at the time, and was sick of the constant false alarms on my radar detector - it didn't even register consciously anymore, and when I found myself driving past a genuine speed trap without taking any note of the warning, I thought it was time to retire it.
So I reckoned cruise would stop me hammering it down the motorway (it hasn't worked on the Laguna, but you can see the logic) and duly spent over 200 quid on a cruise control kit.
Most of it was easy: Strap a couple of magnets around one of the CV joints and park a speed pick-up
next to it. A few simple connections for power and to pick up the brake light feed and a switch on the back of the clutch pedal.
Then I had to try to find a vacuum feed for it. As luck would have it, there was a pipe off the intake manifold that didn't seem too important (I think it was for
vapour recirculation) - I took that off and hooked it into the servo to try it.
What I had was cruise control that would just about engage in top gear at 30mph. Any faster than that, and the throttle was open too wide, meaning that there wasn't sufficient vacuum in the intake manifold to run the cruise servo. I contacted the supplier, and they told me I needed to have the manifold removed and tapped - it sounded expensive and potentially warranty-voiding to me. With hindsight (and knowing then what I know now) I could probably have teed it off the brake servo feed pretty safely. At the time, I was too paranoid to tinker with anything to do with the brakes.
So that was it. Over 200 quid on a cruise control that never worked. I didn't even bother to take it off the car when I got shut.