The brakes?
You might want to ensure that the handbrake is completely released; you might also check the brake fluid level.
Check the brake light switch adjustment.
Sometimes it's the Emergency brake, sometimes it doesnt go all the way down. I had to pull, it release it, pull it, release it etc....
Check the brake light switch. It's probably attached to the brake pedal, under the dashboard.
The dashboard brake light usually indicates a differential pressure malfunction between the two sides of the master cylinder, or that the emergency brake is on. Check the emergency brake, then check the master cylinder. You may need to bleed the brakes. You may need to reset the master cylinder, although they usually reset by themselves.
For a 1988 Jaguar XJ6, you should use DOT 4 brake fluid, which is suitable for the vehicle's hydraulic brake system. It's important to ensure that the brake fluid is of high quality and meets the manufacturer's specifications to maintain optimal braking performance. Always check for any contamination in the system and replace the fluid if necessary.
You have a hole in your brake line.
Lots of bizarre possibilities - but the one you should check out is: What if your hand brake cable is frozen, holding the hand breaks on? This will wear out your main breaks (or at least the rear ones) ... as well as lower your mileage.
Check your car handbook about the brake lights which should light up on the dashboard if the brake pads are worn. If the brakes are noisy and screeching it may suggest worn out pads. You will have to jack up the car and take the wheels off to inspect the brake pads to see if they are worn out.
Check the level or brake fluid in the master cylinder Make sure parking brake is fully released
Check the fluid level in the master cylinder.
check your brake pads