Hey Gang -


Got a message that said "Brake light failure [drivers side] yet all three brake lights work. The turn signals work, the hazards work and the driving lights work. How do you fix what is not even broken?


Maybe it is a bulb that is about to fail?


Turning the car off/on a couple of time did not fix the problem, the message is still there.


Thoughts?

 

Check the ground point on that side. It may be causing a high enough resistance to give the alarm but still allow the light to work.

 

But if the bulb is working, doesn't that mean the ground is correct? What exactly in the ground am I looking for?

 

Look for a loose or dirty ground connection. Both of these can cause a high enough resistance for the alarm to be triggered but will still allow the bulb to work.

 

Here is a pic of the wires...which ones are the ground wires? Sorry but I am not familiar with this car.

 

The tail lamp wires are not directly accessible from inside trunk, unless you open up the wiring loom, but that would not show the resistance problem if it is actually the connector that has some corrosion.
The wiring loom is visible in your picture. It is that black wrapped wire bundle, just to the left of those two connectors in the upper right of your picture. It goes up, and out of view in your picture, before exiting the vehicle.
The electrical connector is outside the trunk, between the car body and the back of the lamp unit.

To actually test the ground, you need to remove the lamp housing (being VERY careful to not break the pointy tip of the housing). You can refer to the shop manual for the steps involved, or download George Kale's instructions for upgrading to LED tail lights (see post #51 in this thread: https://www.jaguarforums.com/forum/x...s-36907/page3/ ), as he describes the steps also.

The ground wire is Pin #3 in the tail lamp electrical connector (and is the black wire in the wiring loom). (For completeness, pins 1 & 2 are the tail lamps, pin 4 is the stop lamp, pin 5 is the turn signal, and pin 6 is the side marker.)

Once you have the tail lamp unit off, you could remove and replace the bulbs (kind of wiggling them in and out), just to make sure they have a good connection, as there might be a bit of corrosion between the lamp base and the socket, giving some added resistance.

 

Thank you for the excellent input. I will try the path of a new bulb first. Anybody know the part number for the rear brake bulb from Jaguar?

 

Mike: I am putting this warning light issue together with the hard starting you mention on another thread and I think perhaps you have had other issues?
I am beginning to think - no, let me be more direct: battery voltage. The vast majority of xk complaints boil down to a battery issue and the symptoms are truly random and definitely include warning lights for no apparent reason. So, how old is the battery? How much highway use does the car get now? Are you using a battery maintainer like CTEK?
And to pick up on your mention of Techron in another thread, yes, this will help clear the injectors but what fuel brand are you using? It should be a "top tier" brand like Chevron or Shell, 91 octane minimum, with a high detergent additive content. But as I said above, the poor starting May in fact be an electronic rather than a direct fuel issue...the fueling is controlled electronically!

 

Dr.A ,
You might be spot on right. I have been having a bunch of wacky issues lately. I do not know how old the battery is [but I will find out] and it does not get much highway use at all. Right now it is just an occasional grocery getter. I have not been using a battery maintainer either. I was under the impression that I should not "need it" because nothing should be draining the battery when it is parked and locked for the night...but I might have to consider it now. I bought the car from a person in Florida who did plenty of highway driving [which might explain why he never needed a battery maintainer]. I am using Exxon Supreme regularly. I will look into the battery situation first thing and report back.
Can you tell me which CTEK model you use for you 2007 XK (and any extra parts/cables as well)


As always...thank you for the input.

 

The CTEK I have is the 7, I also have the 10. They come with all the connections that you will require.
The manual will show you exactly where to connect it correctly.

 

[QUOTE=michaelodonnell123;1408675]Dr.A ,
You might be spot on right. I have been having a bunch of wacky issues lately. I do not know how old the battery is [but I will find out] and it does not get much highway use at all. Right now it is just an occasional grocery getter.

OK Mike: I am certain now that you have a (THE) battery issue, and probably only a battery issue. It is hard to get people to accept this because the symptoms of low voltage output are so random - they happen in every electronic system! There is probably nothing at all wrong with the car itself - the XK is just about the most reliable car Jaguar has ever produced (I have this from several Jaguar techs as well as my own experience) but all modern Jaguars are excellent in this regard.
Don't mess about: get a new, proper battery and get a CTEK maintainer - as long as you get the 12V model, any CTEK 12V model, all will be good. I use different ones, from the most basic to the multistep units - they all do exactly the same thing: they keep the battery at full charge all the time. Do buy the "comfort extension" which allows the unit itself to remain outside the car for monitoring. If you put it inside the trunk you will never think the battery is charged because just touching the trunk release sends the CTEK into operation. *On your 2007 car you can connect the CTEK unit directly to the battery terminal fittings*

 

If you should decide to replace the battery. Look into getting the appropriate AGM battery (Interstate is a good one) as many people on the Forum have suggested AGM batteries for better life, etc. They cost a little more but are more reliable.

 

I'm using the MUS4.3 8 step unit with battery/starter and alternator tester integrated into the unit. Have it set up so I just have to plug it in after a drive . Works out pretty good. I have the unit with velcro on my lift post (on the left) and plug the unit into my Cigarette adapter which is wired to the battery and a separate ground.

 

Went to the dealer...got a Jaguar bulb, popped it in and all is good now. The old bulb must have been going bad...error message is gone.