When troubleshooting an inoperative cruise control system in your Series III XJ6 Jaguar, there are a few common problem areas to inspect. Fortunately, these are typically easy and inexpensive to repair. If your cruise control isn’t working, here’s a checklist of items to investigate:
- 1. Rubber Bellows of the Vacuum Unit: Check if the rubber bellows are cracked or split. If they are intact, ensure they seal properly around the metal endplates. Using silicone sealant can help secure a tight seal.
- 2. Brake Pedal Disconnect Switch: Inspect the disconnect switch at the brake pedal. This switch deactivates the cruise control when you press the brake. Sometimes the wires may break or become disconnected, so ensure everything is properly connected.
- 3. Vacuum Supply Hose: Make sure the vacuum supply hose connected to the bellows unit is intact and securely plugged into the intake manifold. A loose or damaged hose can cause the cruise control to fail.
- 4. Set Switch Electrical Ground: The “set switch” located at the end of the turn signal stalk can sometimes lose its electrical ground. To restore it, remove the lower steering column cover, wrap a small wire around the turn signal stalk, and connect the other end to a grounded screw. Afterward, replace the cover for an invisible repair.
- 5. Sticky Solenoids: The solenoids at the end of the bellows unit can sometimes stick. Remove the black caps and spray penetrating oil into the solenoids. Allow the oil to sit for a while before testing the cruise control again.
If these steps don’t resolve the issue, you might be looking at a more expensive repair.
List Member Insights:
Forest Gibson, a fellow enthusiast, mentioned an additional point that could cause cruise control failure, which isn’t covered in the usual checklist:
“On my ’88 XJS, the lower end of the shift selector operates a pair of cams that control two micro switches mounted just below the console. One switch prevents the starter from operating if the selector isn’t in NEUTRAL or PARK, while the other cuts off the cruise control if the selector isn’t in the DRIVE position.”Jose Maymon added valuable input regarding the cruise control system:
“In my experience with Series III XJ6, I found that if the combination Reverse Lamp/Start Inhibitor/Cruise Control Activator Switch, located in front of the gearshift under the ‘Ski Slope’ cover, is not properly adjusted to the ‘D’ position, the cruise control won’t activate. This switch works in conjunction with the ON-OFF switch behind the gearshift lever, and interestingly, it’s reverse-wired—’off’ is actually ‘ON’ for the cruise control.”Jose Maymon later provided a correction (dated 06/20/2004) to his previous comments:
“I previously mentioned that this microswitch was related to the Reverse Lights, but after adjusting the Gear Selector Cable in my 1984 XJ6, I discovered that the Reverse Lights are actually controlled by a transmission-mounted, cable-activated switch, not the microswitch I referred to. My apologies for any confusion. It’s worth noting that there’s some inconsistency among models, as some Jaguars have a 3-wire microswitch that might indeed control the Reverse Lights, while others, like mine with a 2-wire microswitch, do not.”
See our Jaguar Parts Store Catalog to order parts.
