Gentlemen,
Going to the knowledge well again to drink fully. I look forward to being able to payback with same.
I have been bringing my 89 XJS back to life after a 15 year hibernation...long story...
Got it running and drivable sans exhaust, and decided to farm out front calipers install with new rotors and bearings. Have gotten the car back and have noticed the brake lights staying on continuously while running. I think I would have noticed this before so I suspect there is some correlation with the new parts install. It has ABS with Teves. Used to know this car so well, but I can tell it's going to take some time for us to re-acquaint.
Don't really know where start... So any help you might have in diagnosing very appreciative.
Thanks all

 

I be inclined to begin by disconnecting/wiggling/checking/adjusting the brake light switch at the pedal and see if anything changes.

Cheers
DD

 

Hi Platinummaker

Exactly the same thing happens on my 1990 XJS 'The Ice Princess'

This is because I have taken the ABS Master Cylinder Actuator right out of the Car to have it rewired and haven't got around to putting it back yet

Though before I went any further with this restoration of a Car that hasn't run for years, I wanted to make sure the Engine ran

And so before I tried to Start Her, I pulled out the Fuse for the ABS and also the Fuse for the Brake Pump

Or I could have had residual Brake Fluid squirting all over the place

When I pulled these Fuses out, the Brake Lights came on and they stayed on, which in my own case was what I expected

So start by Checking these two Fuses as they might be dirty or have Blown, then also check to make sure that all the ABS Plugs are clean and plugged in

Though as Doug says it could be the Brake Light Switch

But there is also a fuse down there that could have something to do with it, so check that first



Under the Passenger Side Knee Panel (UK) Car are the Fuses for the ABS and Brake Pump



The Fuses for the ABS and the Brake Pump, make sure these haven't Blown

(Both clearly marked which ones which)




Check that Fuse

 

There IS a brake light relay, downstream of the brake light switch, that ties-in to the ABS circuitry.

I've never studied the circuit so I can't comment intelligently....but a problem or mistake in the ABS circuit could conceivably cause a problem with the brake light circuit.... and blown/missing fuses can create weird feed-back scenarios.

Cheers
DD

 

Most likely the switch at the brake pedal. I had all kinds of problems with the one on my 1990.

 

The 89 has a brake light relay as Doug mentioned, it goes to the ABS ECU and Brake light failure unit and the Brake Lights.

The ECU connection I suspect is an input to tell the ECU the brakes have been applied.

The fault would most likely be in either the Brake Light switch on the pedal or the brake light failure unit. Disconnect both and see if the lights go out.

This might help

 

All,


My appreciation to the combined group. As was suspected by all, it was indeed a broken brake light switch. Have it replaced and all is well...rrr ..well on to the next project!
Many Thanks