Finally replaced the bellows and my cruise worked as it should. Recently, while in cruise on the highway, it suddenly dropped out, as if it had been selected off or I'd hit the brake. It would not re-engage. A week or so later, just for fun I attempted to set a speed and "Voila" it worked. I figured perhaps I'd touched the brake pedal when it dropped out initially. 15 minutes later - it dropped out again! Now it will not engage at all.

So, I plan to check the brake disable switch, then the center console "Select" switch and then the transmission enable switch. My gut tells me it's not the stalk select switch.

I think there are two fuses, #11 and #12 in the main fuse panel that I'll check and roll. but they should not be "intermittent".

Pity there is no "Cruise selected ON" dash light. It would save looking down on the console to check the status.
Ian

 

I have a cruise issue too...pressing "SET" causes the car to accelerate until I hit the brake or turn the cruise off.

Have you seen this: Cruise Control

 

The article which Greg linked will tell you all you need to know.

From memory, one common problem is the release switch at the pedal becoming worn. The innards begin to flop around and the contacts short out against the metal case. But I think you'd find a blown fuse if that was the problem.

Also common is the solenoid valves in the servo. They have rubber sealing pads which can wear out. EZ fix.


You could remove the wonder by simply leaving it 'on' 24/7/365...as I do.

Cheers
DD

 

could be a bad control box They DO go bad. The control box is located under the dash in the passenger side in LHD cars, the knee panel must be removed to see it. There are two versions, the Blue label and the Red label versions, I don't know but I think the Red label version is a redesign in the late cars? Substitution is the only way to find out.

 

do a tiny LED somewhere? I did it to my 1965 S type's Speed Control Switch ( which is not a Speed Control at all), but when the Switch is in the ON position, the LED lights up.

 

Considering just this Jose.

 

another possible cause are the two solenoids located in the engine compartment at the Cruise Housing itself.

 

So 6 weeks after my cruise control started dropping out and 6 weeks after doing nothing to fix it, today I decided to take a 90 min drive to Toronto.
reversing out my wife says "your brake lights are not working", so scapped that plan.
Couldn't figure out what was up but figured it was the brake pedal switch out of adjustment
After opening the switch and finding nothing wrong, wrong in the pedal box and a very pissed of wife saying On, Off, found an intermittent connection to the lights.ed S57
Fixed that with a bit of solder and alls well with the lights.
took her for a spin and Voila, my cruise is again alive.
checked S57 and that brake switch is a cruise cancel backup switch also.
So pleased with killing two birds with one stone.

 

Not my experience!!! Two switches at the base of the brake pedal. Opposite function

One for brake. Open til the pedal is depressed.

Another for CC. Closed til the pedal is depressed. CC circuit interupted, car drops out of cc...

Carl

 

Right, two switches, but the one that is supposed to operate the control cancel is the brake light switch. The other (with YW wires) is a backup to the proper controller cancel mode. They are supposed to sequence, brake switch first, then the backup opens. The brake light switch operates the output transistor in the controller and drops output power to the actuator by dropping the signal to the switching transistor. The backup switch opens the circuit to the actuator in the event that the controller does not properly respond to the brake switch. The problem is that if the circuit is opened while being powered by the transistor there is some sort of surge thru the transistor and an adjacent diode. It will take it for a while, but can eventually burn up and fail. If the cancel switches are correctly setup, the backup switch opens the circuit only after power is removed by the controller and avoids the surge.
It happened on my car. Speed control worked, then it didn't (a recurring theme thru out the car). The output transistor and diode was burned, to the point that the solder connection was melted on the diode. I checked the switch sequence and the backup switch was opening before the brake switch. It had been that way since i got the car and finally failed.
The correct setup is described in the instruction that accompany the AE Installation Test unit. It's also described deep in the long Jag-Lovers link "Cruise Control" posted by Mkii250 above.

 

Loosing vacum? Decades ago, on another critter, it took place. I thought long and hard. It never happened again. Only logical was vacum loss. Once common in the old days. vacum operated wind screen iwipers.

Or. The oter switch under the brake pedal Default is closed. Apply pedal and it opens.

Carl