I have a problem with the brake light switch when I press the clutch peddle the brake lights come on I understand that this I common fault if the break light switch is failing. I have purchased a new switch from a jaguar main dealer part number : C2S46705 . On installing the new switch noting on the brake does not work so I have to put the old switch back in to the car and the same fault occurs. I have tested the new switch with a multi meter with the plunger pressed in and out and I am getting no readings on the new switch. As any body else had this problem or can any one please advice me on what is happening and is their a fix for this this simple job has turned in to a night mare.

 

Ian, the brake light switch should be a very low resistance (under 5 ohms) when it is just sitting on the counter. If you measure across the contacts and push even a little bit on the switch plunger, you should see the resistance rise to something very high (over 200K ohms). In your case, if the switch is reading a very high resistance just sitting on the counter, then you have a bad switch. You need to get another one.

If you are depressing the clutch and this is causing your brake lights to come on, you either have your foot too far to the side and you are catching the brake pedal with your foot or you have something that is getting in the way of the clutch pedal and that is pushing on the brake light switch, causing it to get pushed away the brake pedal (causing the switch to close and light the lights).

The best advice that I can give you is to have someone help you and in short, you need to have your head in the footwell as you depress the clutch pedal. You will need to pay special attention to the area between the clutch and brake pedal to see what is moving, causing the brake switch to be moved. If your assistant says that when you do the clutch by hand that the brake lights do not come on, then odds are, a foot is what is hitting the brake switch and tilting it to the side, causing the brake lights to come on.

The only way for it to be electrical is to have bare wires on 2 wires that as the clutch pedal is depressed, you are pushing these 2 wires together. But, normally, you are going to find that you are going to blow a fuse when something like this happens. The odds of having 2 wires (a power wire and a brake wire) loose their insulation and not touch something metal under the dash is almost unheard of. But, this is where depressing the clutch and watching what happens under the dash is going to be crucial. If you are by yourself, then you might be able to use a cell phone to record things. But, you may need to do it from different angles so you can see on both sides of your foot to see what is moving that shouldn't be and you may need to add some light down there to get a good view.

 

Ian,

What year X type do you own?

It appears that the part number you provided (C2S46705) is for 2007-2008 from Vin J502541.

The part number for 2001 - 2006 To Vin J02540 is C2S3680

Looking at the wiring diagrams for 2001 - 2006 and then 2007 - 2008 it appears that the pins in the brake stoplight switch connector (PA3) to supply power to the switch was changed from pin(-3) in pre-2007 to pin(-2) for 2007 and beyond. (See attached)



When testing the new brake stoplight switch using your multi-meter did you mean that you are getting infinite resistance between the two wires all the time, regardless of whether the plunger is pushed? Or do you mean that with the new switch hooked up in the car, you are testing the output and getting no voltage? If you have the wrong switch installed, you would not get any voltage on the output, since the new switch expects supply voltage to be on pin 2, but the old harness is supplying voltage to pin 3.....

I could be wrong, but that is how I read the drawings...

Good luck.