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MG MGB Technical - CCS-100 Cruise Control Won't Work

I've been messing with this unit for a few months now and can't get it to work. Here's what I've done.
1) I installed it with the magnet on the drive shaft, but using several different dip switch settings couldn't get it to engage.
2) I've made the recommended checks in the manual. The light in the unit comes on when the brake is pressed down, the 'set button' is pressed, the 'resume button' is pressed and when the motor is running it flashes.
3) With the ignition and the unit 'on' the green wire reads 12V when the 'set' button is engaged and the yellow wire reads 12V when the 'resume' button is engaged.

Here's what I'm not sure about...
1) I'm using a pertronix (spelling) unit in place of the points. Is this a problem? By the way this is in a 74B.
2) I have the extra vaccum cannister. I've connected it to the vacuum line that runs from the intake manifold to the charcoal cannister. (as I recall this pulls fumes from the gas tank). Should I instead connect it to the vacuum advance hose?
3) I now have dip switches 1 and 7 on, the others are off. I believe this will allow the unit to take its input from the coil rather than the magnet on the drive shaft. I left the wires connected to the drive shaft pickup. As I recall I disconnected them once but it didn't make any differnece. Should I do something else with the wires running to the magnetic pick up - a grey and black wire if I recall correctly.

I'm stumped but really want to get this working. I have a problem with my right leg and the pain gets hard to take after an hour of holding down the accelerator so I really need to get this working for those longer trips.

Your thoughts and suggestions would sure be appreciated!

James Budrow

I use one of those for my 72 midget. With my header's collector right under the heel of my accelerator foot, trips are much more comfortable with a cruise control...

1. Yes, Pertronix works fine with it. So does 123/Mini.
2. Yes, you do need the cannister if your state is not flat (Illinois is not flat enough for a Midget not to need the cannister). You do want it to have direct manifold vacuum.
3. Do not bother with the driveshaft magnet(s). If you think about it, in high gear that will give you one pulse per revolution of the driveshaft; the coil gives you twice as many. I found on my Midget that using the driveshaft magnet the cc would work fine right up to 60mph, then drop out. With the coil it works fine over 80. I do not recall my switch settings.
David "cruisin" Lieb
David Lieb

Thanks for your comments David. Changed the vacuum hookup but still didn't work so I broke down and asked for help from Audiovox. The tech guys were very helpful. They suggested that I check or do the following.

1) Be sure the vacuum line has at least 14" of vacuum.
2) Adjust the cable/chain so there is no slack but not so tight that if changes the idles speed.
3) If all else fails disconnect the purple wire from the negative side of the brake switch and run it to a good ground. (Note - the cruise will not shut off when the brake is applied.)

I have no real idea why but #3 got the cuise working. Somehow the purple wire is sensing that there is a very small voltage on the negative side of the brake switch. Interesting since the purple wire itself shows a voltage when not connected to the brake switch. Audiovox tech said that it's suppose to.

So now I know that the unit works but not sure how to get it to deactivate when the brakes are applied. Any thoughts on why there might be a very small voltage on the negative side of the brake switch?

James Budrow

This thread was discussed between 29/06/2009 and 11/07/2009

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