I’m back with another gremlin. Grab your popcorn. It’s a good one.

The passenger side (US Right) tail lights probably have always been wonky since we bought the car, but probably didn’t realize it until the High Mount Stop Light went out. That’s now fixed. Since then however, we’ve noticed that the turn signals on the right hand side are dimmer than the left hand side turn signal. In addition, I’ve noticed that the right turn signal also faintly activates the left turn signal. When the passenger turn signal is activated it almost acts like the hazard lights are faintly (not fully powered) activated.

So I went into the electrical manual and did some digging around. It looks kind of wild. I’m not the most skilled in electronics, but I know my way around.

Take a look:




On the left side (driver) I’m getting voltage on pins 2, 4 (weird), and 6. All of the lights behave normally on the left (driver) side.

On the right side (US passenger) I’m getting voltage on pins 1 (CA68-1) and 4 (CA68-4). I should be getting voltage on 2 & 6. It’s on this side where I’ve noticed the weirdest behavior. Those red question marks are 0 volts. There should be power on those two pins.

Note, I did change the wire on CA68-4 to CA63-10 because I was seeing high resistance between the contacts. My concern is that wire may have been part of a splice and perhaps that rerouted the power in. Maybe that’s why I’m not seeing power on pins 2 & 6? I find that to be unlikely, as these problems were an issue prior to changing that wire out. I replaced it because I thought it was the problem, but nothing changed.

Anyway, besides the change in that wire. Everything else has been the same and untouched since I bought the car.

I did see that the right and left side marker lights are burnt out, and I’ll be finding replacements for those. Also, the license plate lights work.

The behavior that is the most weird is the behavior when the headlights are activated. When the brake is activated the right tail light goes completely out. The right reverse light also doesn’t illuminate.

Any ideas on the best way to straighten this out?

 

Oh, also the circles on the right with the “S” and the number. Does anyone know exactly what those mean? Are they splices? How do I dig deeper into those?

Thanks!

 

The Electrical Guide (under Symbols and Codes) shows them as Switched System Power Supply ...

 

You did not mention doing so, but checking to make sure the correct bulbs are installed is always a base-line step in troubleshooting issues in the tail lamp assemblies. "Close" is no cigar when it comes to having the correct bulbs installed; bulbs that will fit pin-wise but are not correct spec will cause all sorts of "wonky" behavior...

 

@S-Type Owner - Yes, I have been thinking about this. I suspect that a previous owner messed around trying to figure out the tail lights and it turned into a cluster. They also fitted an after market alarm system to the car. Dumb.

Is there a list of bulbs that have been confirmed to work on the s-type?

The bulbs is one thing, but with both of the connectors disconnected, why would I be getting voltage in the pins where voltage shouldn’t be recorded? That’s the weirdest part.

 

Remember that the car provides power to (each thing) and activates (the thing) by switching to ground.

 

Yes, understood.

Im still trying to understand the power sources. And why those other pins are receiving voltage instead of what’s supposed to be getting voltage on pins 2 and 6.

I feel like a Neanderthal trying to figure that out. I guess I’ll start digging into F53 and work my way towards the tail light.

Anyone else have any ideas on how to best approach this?

I’m also having a tough time sourcing confirmed tail light bulbs. Does anyone have a source for those?

Thanks in advance.

 

@JagV8 Is “switched system” referring to a relay?

 

We’re getting closer. I went digging into F53 and had noticed that there was a decent amount of resistance on the F53. The fuse wasn’t blown, but you could see a hairline crack all the way to the side. It passed continuity but not resistance.

long story short was a false positive on F53. Replaced and we have most of our lights back.

I went back to the right plug to check the voltage on the pins.

I now have voltage on pins 2 and 4. I’m so damn confused as to why 4 is getting voltage and not 6. And how in the hell does the voltage switch from pin 1 to pin 2 after replacing the fuse? Fundamentally something isn’t clicking as to how that happens.

As of now - no reverse light, faint right blinker that activates both sides faintly. Everything else works as it should.

I’m waiting for the rear side marker W5W bulbs. I can’t imagine a W5W bulb messing with the tail light, but as this point I wouldn’t doubt it.

Thats the update for today. 😂

 

I think so mostly but could also be via a module.

For a particular power source just follow it through the Elec Guide pages if you want to find its source.

 

On voltages being where you don't expect (or absent), a wrong bulb could be shorting somewhat and thus powering something it should not be connected to at all.

 

Per your request:

 

Those are not splices. They are legends for navigating between pages within the wiring diagrams.

Having trouble opening the wiring diagrams at the moment, but I think at the bottom of each diagram you'll find a key explaining those legends. For example, with the S and number within a circle, you'll be directed to another page, typically near the front. There you will find that same number, showing the rest of the circuit. IIRC, some of the other legends are a plain circle (no S), a square, maybe a square with a B, and I forget what else.

I think the square stands for battery power, meaning power is always present even with the key switched off. Can't remember exactly what the B means, but it has to do with battery power. The circle stands for switched power, meaning power is switched on or off remotely, either directly via the ignition switch or indirectly via some relays. I think the S means relay controlled, but don't quote me on that. I believe there's some content near the front of the wiring diagrams explaining all these details.

 

Are you using a digital meter? In some cases, they can be too sensitive, showing voltage present where you wouldn't expect it, which can be VERY confusing.

As others have mentioned, Jaguar uses a switched ground method of control for these lights. The right side of each diagram shows battery power to each bulb. Towards the left, you'll see the control module which provides a ground when commanded to complete the circuit and illuminate the bulb. Seems simple enough, even if a bit backwards, right?

Things can get a little confusing if your meter is too sensitive, of which most digital meters are guilty. Instead of a mechanical on/off switch controlling the ground, it's all electronic magic inside the module. And a sensitive meter can pick up a stray source of voltage where you'd expect to see either a ground (bulb on) or an open circuit (bulb off). This stray voltage basically means nothing and cannot perform any useful work. It's just there to confuse the troubleshooter, self included. To give you a rough idea of how confusing this can, set your meter to AC voltage and hold the leads in the air near a fluorescent light fixture. With the light on, a digital meter will typically show AC voltage even though the leads are not connected to anything but air.

Some of the individual bulb circuits also have a monitor function, to alert the driver to a burnt out bulb. Just a guess, but I think the module looks for continuity through the bulb when off, and a certain amp draw range when on. This monitoring function can really skew the results if checking voltage with a meter.

There could also be a problem with the power supply to each bulb. Let's say a multi-strand wire has a corroded crimp somewhere, and only one strand is making good contact. That single strand will flow enough current for the minuscule draw of the meter, and lead you to believe proper voltage is present. But when the circuit is under load, this poor connection falls down and the bulb barely illuminates, if at all.

How to get around all these factors? I'd suggest using a 12V test light with an internal bulb. This puts a slight load on the circuit and simulates real world conditions.

 

Another issue to consider is with bulbs that have dual filaments. It's possible for a filament to break and then touch the other filament, often welding the two together. Now when one filament is supposed to illuminate, it can send power into the other circuit and create all sorts of havoc.

Edit: Forgot to mention sometimes a bulb which has failed in this manner can still illuminate to some extent. This really throws a wrench into the troubleshooting process. When you see a bulb light up, it’s easy to (incorrectly) deduce it’s good and look elsewhere for the problem.

 

@kr98664 Thank you for the thorough and thoughtful response, I’m mostly tracking. The only thing that trips me up is that with both of the tail light connectors removed I’m getting 12v in the wrong places. As you mentioned I should be getting voltage on pins 2 and 6. There are no bulbs connected to bridge power to the other pins. So my question is… Should I be looking for a wire? A relay? A bad splice?

I will start with the test light and see without the other bulbs if things are working.

The other thing I would note would be that I can take the whole tail light assembly and connect it to the other (driver) side and it all works as it normally should.

it feels like a relay problem. The ground is super clean. No corrosion whatsoever so ever for the one that’s in the boot. Maybe there is another one that I should be looking for?

 

Thanks for sending along. Is there a specific brand to use?

 

Okay, I put on my orthopedic thinking cap. For a bit of history, I looked at your previous thread about the high-mounted stop light misbehaving:

https://www.jaguarforums.com/forum/s...issues-278419/

From your initial post there:


You eventually changed the Rear Electronic Module (REM) and operation of the stop light returned to normal. Problem fixed, or so it seemed. After replacing the REM, when did you notice the new issues with these other lights? The clues seemingly point towards the replacement REM being defective. Do you still have the old REM? Sure seems worthwhile to plug it back in for troubleshooting.

 

My personal preference is Phillips-Osram because they have plated metal bases that don't corrode readily if exposed to moisture.

 

@kr98664 I did consider that. I do have the old REM and I did disconnect the new REM and reconnected the old REM and the right tail light behavior was the same. No reverse light and a dim turn signal that activates the left turn signal as well.

While testing the tail lights prior to the HMSL issue I do remember the turn signal being light being dim I didn’t think to much about it, but after the fact the reverse light caught my attention and I realized that the left turn signal was also faintly activating the right turn signal.

Regarding the REM, I had my suspicions too, and I ended up buying another REM off of eBay to test out. I think that arrives today.

I’m going to get in with a test light this evening and I’ll let you all know what I find.

I’ll take another look at the diagrams to see if I can understand the switchable power or if there’s a relay that might be root of the problem. So bizarre…