I have an aftermarket cruise-control system which only somewhat works in a 2005 Ford Focus.

By this I mean that it controls the speed but is largely inaccurate (+/- at least 10mph). Going up/down hills causes the speed to slowly increase/decrease for a long while. So it works... somewhat, but, obviously something is broken/failing with the system.

What can I do to diagnose the problem?

It looks identical to this product. I do not know the exact model because it was installed prior to me purchasing the car.

Here are some pictures on console

I think this is the unit under the hood (I'm not sure though...).

what I think is the unit under the hood

  • It's an aftermarket product, how do you know it just isn't designed to work well with your ford? Dec 28, 2012 at 20:47
  • @hillsons it used to work a lot better
    – enderland
    Dec 28, 2012 at 20:52
  • Any idea what brand the unit is and have you changed your brake lights lately?
    – mikes
    Dec 29, 2012 at 1:28
  • I need to know the type of system, does is use a vacuum servo, or electronic? The name and model number of the system would be a great help. Dec 29, 2012 at 19:42
  • @mikes I added pictures and a link to the question. I have not changed brake lights recently (or ever).
    – enderland
    Dec 29, 2012 at 19:56

1 Answer 1


It appears to be a Rostra unit their site http://www.rostra.com/rostra-support.php has an extensive support page. That is why I asked about the tail lights, they mentioned it. I would go to the site input you vehicle info and click the support tab. They will give you step by step instructions included are calibration steps, which may be your issue.

  • oh wow. I had no idea they had that much information there, guess I'll be reading and hopefully be able to find the needle in that haystack...
    – enderland
    Dec 29, 2012 at 20:18

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