cruise control for a street rod

What are you using to provide a speed sense output?

I am using the magnet attached to the drive shaft. The unit was working and then stopped and I do not know if it is the vacuum or what??

Is the magnet still on the driveshaft?

Yes the magnet is still attached and I checked to see if it was still magnetized and it is. After troubleshooting the unit it would work for maybe 30-45 seconds and then quit which is why I was checking the vacuum. I checked all of the wiring with a volt/ohm meter and the wiring checks out perfect. I had the unit run thru a stalk on the steering column and thought there might be a bad wire and installed the Dask mounted control switch. I then set the dip switches accordingly and the unit worked for about 1 minute then quit. It really has me puzzled.

The symptoms are sounding like a vacuum leak. It has been many many years since I have had any hands on experience with a cruise control.   I wish I could be of more help.

To test for vaccum, just unplug the hose from the cruise with the engine running. The engine idle should change slightly. If you put your finger on the end of the hose you should feel a small amount of suction but not necessarily enough to keep it stuck to your finger. I know you said that you did an electrical check, but almost everyone gets it wrong on Rostra cruise controls. There are 2 very important things to check. With the ignition OFF, use a digital volt/ohm meter to check the resistance to ground on the black ground wire and the violet brake wire. The black ground wire should have less than 1 ohm resistance to ground. The Violet brake switch wire MUST have less than 10 ohms resistance to ground. Most people check the violet wire as having 12 volts on it when you apply the brakes. This is wrong. The violet wire needs to be grounded for the cruise to work. It loses ground when the brakes are applied and the wire is fed 12 volts. It gets the ground through the filament in the brake light bulbs. If one or more of the brake light bulbs don't work or if you have changed them to LED's, this is your problem. You can retro-fit the cruise to see ground on the wire with a relay if you have opted for LED's. Just make sure that you use a digital meter to check all electrical circuits and not a test light. They tell you nothing.

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sparky

After double and triple checking the wiring and installation I discovered that the dip switches were not in the correct order. In order to rest the switches it required that I take the unit out of the car as I could not see the switches with it installed in the car. I then used a pocket screwdriver and reset the switches and reinstalled the unit in the car. I drove the car and the cruise works again. It pays to recheck ALL of the troubleshooting guides as I was ready to purchase a new one and discard the old one.

I am glad you got it figured out.