I have read carefully the previous posts on this apparent common issue with the XK8.

I HATE throwing parts at a problem but after consulting with several I did replace the brake switch to no avail.

All fuses are good.

All grounds are good.

Swapping relays resulted in no change.

When I power probe the appropriate wires related to the stop lights they work.

I removed the alarm module and the light module to look for corrosion or burned spots and saw none, but I have no way to know if wither is good? Is there a way to test the might module or bypass it?

If the light control module is bad, would that prevent the shifter solenoid from working so it can be shifted out of park?

Any help would be appreciated.

 

Perhaps you've already checked these two items:

1. Battery voltage must be at least 12.6 volts when read with a voltmeter with the ignition OFF. What is the voltage?
2. Does gear selector surround light up to indicate gearbox is in the 'P' position when the engine is running?

 

I will check both and report back. Thank you

 

Do I remember right that there are two switches on the brake pedal? I believe one is primarily for the brake light and the other is related to cruise control, and the shifter lock is secondarily tied to both.

I also seem to remember that one switch is normally open while the other is normally closed.

Maybe the brake light switch is working but the cruise control switch isn't, and the car is noticing.

 

If the brake lights work it's time to move on to the solenoid itself. Is there power to it when there should be? Is the solenoid itself open circuit?

 

I thought he said the brake lights don't work unless he forces them with the power probe.

 

Aah! Well I misread that one didn't I?

Well spotted.

 

You might pull the lamp control module (probably located in the trunk fuse box - but I'm never sure given the haphazard way mine was put together). The lamp control module snaps open and if the circuit board is burnt, you will see in immediately or almost immediately.

By the way, when I first bought my well worn '97 coupe, I was not able to get the Park solenoid to disengage (nor did the previous owner who "fixed" the problem with a pencil wedged in front of something or other), so finally bodged it. I believe that I wired it through the brake switch, but it's been years so I don't recall exactly. Anyway, I did this hack before realizing that a previous owner had also removed the lamp control module and soldered all of the taillight wires together. I now believe that the Park release might actually work through the Body Control Module, because I replaced the module. (But it works fine now, so I'm going to leave it alone.)

Lamp control modules are still relatively easy to find on eBay at 25 bucks or so. At least for now.

 

The wiring around the brake switch is common to the two issues.
Note that 6ii and 7ii (WO white/orange wires) route to the ignition switch and are grounded when it is set to position ii (on).



Normally, pressing the brake pedal will close the switch and ground EM10-10 on the ECM connector. The ECM detects this and messages the BPM to release the shift interlock.

Although it's not shown on this part of the wiring diagram, the stop lamp relay also connects to the above circuit at splice FCS35, hence grounding this line will also fire that relay and operate the stop lamps.

I would check for continuity on the US (blue/slate) wire from FCS35 back to the brake switch, and for ground on the WO (white/orange) wire, with the ignition switch on. Alternatively, grounding the blue/slate wire at the brake switch connector. should operate the brake lights.

No. the lamp control module is between the stop lamp relay and the lamps, so downstream of the problem.

 

Just tried anothe rlamp control module which did nothing. I am trying to follow your schematic but the wire colors are not the same. I do not see a white/orange wire? Would it be possible to call you? I'd pay you for your time.

 

Just to have it handy, here's the electrical diagrams for the 1997.
I went to see if michaelh might have posted the diagram for a different model year, and nope, he got the right one.

http://www.jagrepair.com/images/Auto.../jagxk1997.pdf

 

Have continuity between brake light switch blu/slate and #3 on stop light relay,,,

 

OK perhaps there is some variation. The electrical guide states that pin connections may be different on the very early cars, and to rely on the wire colours. It's not entirely error-free so you may have encountered another mistake...

If you can find the black wire on the brake switch assembly itself (I'm hoping the electrical guide has got this one right) then that will work just as well. It should be at ground with the ignition switched on,

OK, then if you ground this your brake lights should illuminate and, assuming there really is only one issue, the interlock solenoid should also operate.
You can do so by running a piece of wire between the blue/slate and the cigar lighter socket outer metal case.

For completeness, here's another snippet from the guide showing the interlock solenoid. In a resting state, there will be no voltage on either connection to the solenoid:

I think the keylock solenoid was deleted early in the production run.

 

Michaelh wrote:
The wiring around the brake switch is common to the two issues.
Note that 6ii and 7ii (WO white/orange wires) route to the ignition switch and are grounded when it is set to position ii (on). PULLED LOWER STEERING WHEEL COVER AND FOUND ORANGE WHITE WIRE. IT DOES GROUND MY TEST LAMP WHEN IGNITION IS ON. I ALSO TESTED CONTINUITY ON EACH END OF PLUG AND IT IS GOOD.



Normally, pressing the brake pedal will close the switch and ground EM10-10 on the ECM connector. The ECM detects this and messages the BPM to release the shift interlock.

Although it's not shown on this part of the wiring diagram, the stop lamp relay also connects to the above circuit at splice FCS35, hence grounding this line will also fire that relay and operate the stop lamps. I GROUNDED THIS WIRE AND THE BRAKE LIGHTS DID NOT WORK/

I would check for continuity on the US (blue/slate) wire from FCS35 back to the brake switch I DID AND THERE IS CONTINUITY, and for ground on the WO (white/orange) wire, with the ignition switch on I DID AND THE GROUND WORKS AS MY TEST LIGHT FIRED. Alternatively, grounding the blue/slate wire at the brake switch connector. should operate the brake lights. I DID AND THE BRAKE LIGHTS STILL DO NOT WORK

 

I probably should have thought of this as a check before the grounding exercise. Do you have 12V on the blue/slate wire if the brake pedal isn't pressed?