I am looking for help with some circuit logic.

The schematic is drawing "Exterior Lighting 9.1" for an X308.

- pin FC-15-20 output, foglamp relay control is defined as active ground
- pin FC-15-16 input, side marker request is defined as active ground

Why would shorting these two pins together result in the side markers being on while the ignition is off and the light switch is off?

The relay coil is powered by 49-ii, which is supposed to be ignition controlled.

When the ignition is on, the foglamps properly follow the side marker position of the headlight switch at FC-15-16.

The headlight switch is a bit of a blackbox because it is the 3 position switch(off, side, low beams) that is used for DRL.

 

1st question - they're not supposed to be shorted together, so when NOT shorted together, does everything work properly?

2nd - FC15-16 is a logic level input, becomes pulled to ground through the ignition switch, or through the stalk switch in 'dip' and 'side' position, and connects through the 'dimmer overide switch' to a bunch of lighting modules... but won't be pulled low unless you've done something (or the module has) to turn them on.

Now, the lighting module gets power from the Battery Bus, non-switched, it's on all the time... so if FC15-16 gets pulled low by anything, anytime, the side markers will come on.

You mention the FOG lamp relay gets power from 49-II, which is ignition powered, but, again, the side markers are driven directly from the Lighing Module, which is, again, always powered. So, lack of power to the fog lamp relay has nothing to do with this issue.

The one thing we DON'T know, is the state programmed for FC15-20 (a logic level output) when the lighting module sees that that key switch is not turned on - fog lamps only work with key on, as you have already described - the relay gets no power without key on. SO, it is possible that the firmware programmers just never bothered to define the state for FC15-20, in a state that wouldn't exist - fog lamps on with key off... and that output (FC15-20) is just default low under this condition (key off) - so a short between FC15-20 and FC15-16 would pull FC15-16 low and turn the marker lights on.

So the question still remains, why are FC15-16 and FC15-20 shorted together and what happens when they're not?

 

a1: everything works fine when the circuit has not been modified

a2: FC-15-16 is unswitched, but the splice in it at FCS9 going to sheet 10.2 has switched elements. In that stock configuration, the side markers go off properly. So, I think it is FC15-20 going to ground with ignition off. It is inactive=B+, but you notice that the supply side of the relay coil is ignition switched. So, it might more be accurately termed a "foglamp inhibit" circuit.

For that situation, I think a diode in the jumper could be the solution.

a$64: it is actually a added SPDT switch doing this. position A is "as designed" position b is "follow side marker" as choices to how the foglamps behave. The problem description was reduced to the bare essentials to avoid confusion.

That is part of a larger scheme to override the poorly designed DRL implementation.

DRL's are proven to reduce accidents. The seminal study was in the 1970's where a Swedish bus company reduced highway accidents by 70 percent just by switching on the headlights and running lights on their fleet 24 hours a day. Sweden became the first country to mandate DRL's.

But, having headlights on while not in motion is silly. Especially when the engine is not running but the ignition is on for a service operation. The reflectors get really hot as there is no air passing over the headlights for cooling.

 

I've added edits while you responded, so I suggest you go back and read again, sorry...

 

Okay, so as I understand this, it is an added DRL issue? I don't have DRL's, nor do I see support in the docs for them (haven't looked hard though).

What is your ultimate goal here and how are you trying to implement it?

BTW, it's late here, in SoCal, and I'm going to bed. I'll return tomorrow. Where are you?

My knee jerk suggestion (again, without much thought) would be to add a relay that inhibits DRL unless the fuel pump is running - use the fuel pump power signal to energize the relay.

 

Thanks for looking.

It's not "added" DRL. It is factory DRL. It is not documented in the wiring diagrams other than "DRL uses crank signal" on sheet 9.1. The crank signal inhibits the headlights to get more juice during cranking. That's the full extent of the documentation.

The foglights at pin FC-15-20 have nothing to do with the DRL system, but since the BCM harness was being worked on, it was convenient to also address the foglamp operation.

As implemented by Jaguar, the front foglights can only be turned on in conjunction with the low beams. They turn off in all other situations.

With the new switch in place, the front foglights can be set to factory behaviour, or to follow the operation of the sidelights. In both situations, the foglight indicator operates to track the on/off state of the foglights.

The beam of the factory foglights is extremely low and wide. Very handy to pick out lane markings in adverse situations. They are also handy as DRL if one is in the habit of turning on lights manually.

solution to problem

It turns out that FC-15-20 actually behaves as if it were a "foglamp inhibit" with active high. And when the ignition is off, it is low. It is not held high because the relay coil supply at 49-ii is already ignition switched.

However, with the added circuit complete to FC-15-16, it is the same as switching on side beams manually because FC-15-16 goes low through the added circuit to FC-15-20. FC-15-16 will operate the side beams according to the signal seen regardless of ignition position. That is why the side beams are staying on with the added circuit.

The solution is to insert a diode into the circuit so that FC-15-20 can be pulled to ground by the headlight switch ground at FC17R reached through FC-15-16, but not vice versa.

additional question

The additional question then becomes whether it is safe to do so.

FC-15-20 is designed to operate as an output with the load of the foglight relay coil. The coil has a resistance that limits current to some degree.

With the added circuit, the output has a path to ground with negligible resistance. Current is then unlimited. The pin is driven at B+ when the factory foglight switch has not been pushed since startup.

If the driver circuit for FC-15-20 has a current limiting resistor, no problem. But, that is an unknown.

sidebar

The headlight operation works as intended in the modification using FC-15-42 and FC-15-68. The options are: "factory drl behaviour" or "follow headlight switch operation". This is done by selecting whether the headlight switch or FC-15-68 provides the path to ground for the headlight relay coils.

 

I thought about DRL's for my car - I know Canadian spec cars are equipped with the system, have you looked into the wiring diagrams for this system?

My answer was to use aftermarket lamps. The lamps have an outer ring I tapped into the sidelights loom to control. Along with high power (5W) SMD led's fitted to the side lights instead of W5W bulbs, the upgrade is highly visible in daylight, it also looks factory fitment, not the usual silly led strips that are becoming all the rage.

The inners are HID, and they're connected to the front fog loom.

The reason, all Euro spec cars produced now have to have DRL's - I understand the use and justification from a safety perspective.

 

@Sean B

The documentation for DRL on the 1998-2003 consists of a single footnote mentioning the dependency on the cranking signal. The drl specific headlight switch is not documented at all.

On a UK spec car you have two additional options not requiring rewiring:

a: drl programmed by dealer using wds

b: leave headlight switch in "auto" position and put a piece of black tape over the sensor on the mirror

But, defeating drl on a drl specific bpm for X308 is quite different. You can switch drl modes for various jurisdictions via wds/ids but not switch it off completely.

The headlights are on as long as the ignition is on. Even when the car is being serviced with the engine not running or the car is not in gear. This is hard on the battery and headlight reflectors. The silvering on the headlights peels and flakes when the reflectors get too hot with no cooling airflow.

If your HID are now on the fog switch, are your fogs now on the main beam circuit? That seems awkward. Is that so you can flash using the fogs because the HID take too long to warm up?

 

@ Plums,

I didn't know the headlights are used for DRL's on a DRL programmed car! I agree it's not the best solution for the reasons you stated.

To clarify, I have HID for dipped beam, incandescent for main beam, and HID for fogs. The systems I used are the micro ballast type. With the BMW H7 lamp holder adaptors for the dipped beam.
They all work from their switches, i.e. fog switch for fogs, dipped for dipped beam etc. A picture of the 'two lamps in one' should show what I mean, the outer ring connected to the side lights, the inner HID connected to the fogs. Angel eyes, on a Jag!?


I wonder if you could go with a non DRL BCM, and tap into the sidelights?

 

I asked the dealer to turn the DRL on on my 01 US specs XJR and it certainly didn't require a new headlight switch, just reprogramming through the WDS

 

Your cat sleeps on a quilt? How spoiled!

That's less confusing now. The add-on is around the fogs, but controlled by the side light circuit.

With respect to the non DRL BCM, that's money and problems with getting it programmed.

And it *still* would not allow the fogs + side light combination without modification.

The last problem of the potential overcurrent is going to be solved with yet another diode in the circuit. And a third diode will get the system to do auto-follow of the headlight by the foglight regardless of position. The harness has to be cut open again. It's starting to look like a furball.

 

Nobody is suggesting that optional DRL requires changing the headlight switch.

It is possible to turn on DRL on a US spec car via wds/ids. However, it is not possible to turn off DRL on a DRL spec car solely by wds/ids. It is only possible to set the pattern required by the various regulations.

In any case the headlight/drl part is done and works fine. DRL was only mentioned as an aside.

The specific problem posted was with the stray current from the non-drl fog light circuit modification that was leaving the side lights energized in the modified circuit with the ignition off. That has since been rectified with a diode.

 

In 1 of you previous post, you state: "The drl specific headlight switch is not documented at all."

 

That entire statement is true. Such a part does exist and is used in conjunction with the drl specific bcm.

However, it was *not* said that a US spec car with a non-drl specific bcm could not have the drl turned on without such a switch. The ability to do so is well documented in multiple threads. This thread is about something else, as clearly stated in the opening post.

This entire thread is about modifications to the fog light circuit. The modification involves tapping a circuit to the headlight switch. The headlight switch is of the DRL variant. Therefore, it was described for the benefit of QuadManiac who I asked via PM to look at the thread. Troubleshooting circuit modifications with many interactions *requires* this level of detail and analysis above and beyond simply looking at the schematics. For example, note that the expected and documented behaviour of each pin involved in the modification is called out by logic level, operation and pin number. And that is only the starting point for discussion on why the circuit is misbehaving.

The fact that a US spec car with a US spec BPM can have DRL turned on has no bearing on the problem that was posed. It also has no bearing on turning off the DRL on a DRL spec system. They are not the same and do not behave the same.

In short, US spec DRL is entirely out of scope of this thread.

 

Not sure where you got your information that DLR use a specific headlamp switch, maybe you can enlighten me?
JEPC only list 2 switchs, both for NA and ROW markets:
LNC6455AA for Auto headlamps
LNC6455AB for non Auto.

I was neither comparing "factory" VS "dealers" DRL nor NA VS ROW DRL, simply pointing out that the headlamp switch is the same

 

@luc

This is post #16 in a thread about a specific technical problem with a foglamp circuit modification. 6 of the posts have dealt with your views on turning on US spec DRL. That is 6/16 or 37.5 percent of the total post count do not address the question posed in the opening post!

Given the clear response at:

https://www.jaguarforums.com/forum/x...76/#post391490

2 posts should have closed the matter.

 

I guess that you're getting upset because you can't back up your statement regarding the use of a specific headlight switch for factory enabled DRL.
Too bad, this forum is there to help Jaguar owners with ACCURATE information and if I see something that I believe is not accurate, I will, for the benefit of this forum readers, point it out regardless of the poster "feelings" or of the fact that it was not the main subject of the post/thread.
On the same subject of accuracy, I do not believe that your statement: "However, it is not possible to turn off DRL on a DRL spec car solely by wds/ids. It is only possible to set the pattern required by the various regulations." is correct.
See this link:http://forums.jag-lovers.org/av.php?1076576i44
It is a Canadian owner of a 98 XJ8 that after being told by many Jaguar dealers that the factory enabled DRL could not be deactivated through the WDS founded out that it was indeed possible.
Other link from a jaguar technician: http://www.justanswer.com/jaguar/3q4...01-jaguar.html

JEPC do not list a different BCM part # for factory enabled DRL.
All BCM are programable with the options/ requirements for different markets

 

Ignoring all the other 'issues' that have been raised during the last 24 hours, let me see if I truly understand what it is you are trying to do -

From what I can see, you want the fog lights to be able to be turned on when just the marker lights are enabled. Is this correct?

A bit more detail on exactly what you want to happen under what conditions would help. What other permutations and combinations of engine, markers, headlights, fog lights are you looking for.

Driving your diode with the FC15-20 output when it is high ('fog disabled' as you describe) into the ground supplied by the headlight switch, as you stated, is asking for trouble. It is certainly possible to isolate this using several diodes, a simple transistor circuit or an additional relay and several diodes... as soon as I fully understand what you want, it will be easy to describe the solution. Until then, I'd avoid your suggested diode circuit - inadvertent damage to the lighting module would be prohibitively expensive.

If you simply want the fog lights to follow the markers, use two diodes - one with cathode to FC15-20, anode to fog relay LF5-8; the other with andode to LF5-8 (the first diode's anode) and the cathode to the marker signal - FC15-16, adding your switch to break this latter connection to return to normal (stock) operation.

With the second diode in place, when the headlight switch pulls FC15-16 to ground (and your switch is closed), LF5-8 will be pulled to ground. If ignition is on, the fog light relay will be energized. If FC15-20 is high (fog lights disabled), the reversed diode will prevent a current path from FC15-20 to the headlight switch. However, if your added switch is open, and FC15-20 goes low (fog lights on), then the relay will be pulled down through the diode at FC15-20 and will be energized... Is this what you're trying to achieve?

See schematic below:

 

Yes, when the switch is in "custom" mode, the foglights follow the side markers. When in "factory mode" it operates as originally designed.

Your suggested placement of diodes is exactly what I ended up with. I first tried the diode towards the bottom of your schematic to eliminate the side effect caused by FC15-20 being at ground potential when the ignition is off. That was a success.

Then, due to concern about unlimited current draw when FC15-20 was "inactive" at B+, I added a second diode where you have it at the top of the schematic.

Finally, having put those two in. I added a third diode isolated circuit from FC15-68 (low beam relay coil) to (effectively) the wire run between the bottom diode on your schematic and the switch leg above it. That causes the foglights to also follow the main beams when in override mode. That addition takes care of the situation when the "drl override" circuit is not in effect, and the headlight switch is not at ground potential at FC15-68.

In the end, everything works as hoped. The only possible minor niggle would be whether the headlights flash when locking/unlocking with the remote. Probably not in "drl override" mode, but normal in "factory" mode.

Thanks for all the time you have spent on this. Your initial and followup posts prompted the consideration of diodes. And, your insights on possibility that FC-15-20 behaviour was undefined with ignition off was the eureka moment.


So, in the end, the car now has "configurable" drl at the flick of a switch, the modes being: factory, side marker/tail light, side marker/tail light/foglight. This is because the bpm, being untouched, remains in drl mode. The foglights can come on with the side markers, headlights and can remain on with the high beams.

The next targets are to have the center switch pack illumination come on with the main instrument pack, and side markers that flash with the turn signals(think 70's GM F-body) when turn signals are active. The hardest part of both is simply accessing the harnesses.

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