Well, I've now tried four different LED bulbs in the high mount (3rd) brake light and only one off brand single chip LED physically fit into the reflector. Even with only one LED chip it blew the 10 amp fuse (position 6, right heel board, "tail lights") when only one of the four 194/2825 bulbs was replaced with the LED.

And none of the multi LED lamps fit, and they'd probably blow the fuse even more quickly

It seems that the hole within the reflector is nearly exactly the same size as the glass 194/2825 bulb, and most LED versions are just a tiny bit larger diameter, enough that they won't fit.

I also tried a single genuine Sylvania/Osram LED whose diameter was too wide but I made fit by opening up the hole in the reflector, but it also blew the 10 amp fuse when paired with the other three incandescent bulbs.

So while there may be an LED that will function (not blow the fuse) and physically fit, I've not found one.

.....not super important, but just an FYI

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Are the LED lamp ends shorting to the reflector?
A LED is not likely to draw anywhere near as much current as an incandescent lamp and certainly not enough to blow a 10A fuse (well I guess the total current through that fuse includes other lamps too). In fact because LEDs draw less current, fitting an LED to replace an OEM lamp can cause a bulb failure warning, even though they are working. That is what happened when I replaced my plate lights with LEDs because the originals had melted the plastic housing.

 

"where" are you buying the bulbs from?

I ask because we should be sourcing from a vendor who understands how to cross-reference bulb types.

I've swapped out all the rear brake bulbs on all (4) of my bikes sourcing from superbrightleds .com. I use the "flash 3 times then go solid red" for brake lights. Next I plan to replace all turn signals. Finally I will replace the headlights (only on the ST and GoldWing - granted, there is only one source for GW specific LED headlights, not SB-LEDs.com). Once the bikes are done, I'll replace the rear facing bulbs on the autos.

SBLEDs understand the cross referencing of bulb type (as in standard bulb type part#) and the "if the bulb color is yellow, use this", "if the bulb color is red, use that".

I wouldn't necessarily "trust" the local auto parts store and use a bulb that's close to spec. The key is to do the research up front, to avoid experimentation.

 

Yep, thanks, but "been there, done that"

I've also replaced entire lighting and instrument clusters on cars & bikes that sometimes really weren't even user serviceable. So I am very familiar with using vendors to source the right part. And as you've no doubt discovered, sometimes LEDs just won't work, or require other modifications such as loading or accessory circuitry to fool other control systems to think an incandescent is still there. For example one has to use an incandescent in my low fuel lamp for my V11 Lemans as the resistance of the lamp filament as it heats is part of the detection circuit and if changed to an LED the low fuel detection simply will not function much less light a lamp. The alternative in that case would be to build a separate circuit that mimicked that behavior. It just wasn't worth it. So every lamp in that cluster is now LED except the low fuel indicator. And my older Kisan signal and tail-light minder/modulators don't really like LEDs either as I recall.

But.... so, in fact, for this application I did buy two different options from SuperbrightLEDs, who BTW I've also used for years.

One multi-LED option from SuperbrightLEDs wouldn't physically fit into the housing (which as an aside, I've found to be the rule versus exception in this specific 194/2825 LED replacement application) so I couldn't test it electrically, and the one SuperbrightLEDs single LED option did fit (although I think I may have trimmed it down around the edge a bit if I recall) but it popped the fuse when only one LED lamp was fitted. I would assume that with four of them the fuse would burn just as well.

I also attempted a generic LED 194/2825 replacement from my local big box auto parts store, but it also wouldn't physically fit past the hole in the lamp reflector.

This last attempt was the most promising however as this was a genuine Sylvania/Osram "Zevo" red 194/2825 single LED replacement that appeared to possibly be juuuust the right size to fit into the reflectors hole AND it was a genuine Sylvania/Osram product which is typically much higher quality than the eBay, generic or even SuperbrightLED import products. However, it was also just a smidgen too wide. So I took a spare 3rd light housing, and with a 1/2" drill bit opened up the hole in the reflector and was able to then insert the Sylvania/Osram LED bulb.... but "poof" the fuse then blew with the one Sylvania/Osram LED bulb and three other OEM incandescent bulbs installed, just as I had observed with the other SuperbrightLEDs smaller LED.

I should also add that since it was an LED this wasn't a polarity/orientation issue, because in both cases with the SuperbrightLED single LED and this Sylvania/Osram, the LED would not light at all when oriented incorrectly. The fuse only blew when the LED was oriented such that it electrically should work.



So does that mean that no LED will ever work in the 3rd brake light location? No it does not. But my post was meant to spark the conversation and point out that my limited testing so far was not promising given two initial observations:

1) So far 75% (I think actually 100%) of all four LEDs tested by me for a 194/2528 bulb application will not physically fit into the lamp housing unless one drills out the reflector hole to a larger size.

2) So far of the two LED bulbs I've tested electrically, both single LED chip units spec'd to replace a 194 or 2528 bulb, they have burned out the 10amp "Tail Lights" fuse in the right hand heel board location. This is with just one (out of possibly four) LED bulb installed.


That all being said, if someone does have a known LED replacement that both physically fits the unmodified lamp housing and electrically is compatible (does not burn the fuse if all four lamps are replaced), that would be great to hear.

Even if someone knows of an LED lamp that electrically works, but requires the reflector lamp hole to be enlarged, that would be great too.

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I still think the problem is not the LEDs. Have you tried the LEDs in a different situation or measured the current one draws?
I suggest the brake light fitting is more likely the problem ie when the LED is fitted the connector is shorting.

 

I understand, I've worked with a lot of LED replacements, so I can't say why it shorting or drawing more current. But then again, remember that there is a control module in between, so maybe that plays a role when the draw is so different with the LED.

But the LED bases appear to be identical to the incandescent bulbs, especially the Sylvania/Osram. They definitely aren't shorting against the reflector, I know that.

I may put more effort into testing at some point, but for now it isn't a priority.

Again, if someone else finds a particular LED that works or why/what the scenario is that can cause the fuse blowing, let us know.

The problem and risk is that when it does blow the fuse, you lose all tail/brake lights, so from my perspective it isn't worth being unsure unless we know for certain why it is happening.

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From the wiring diagram, the taillight brake lamps are driven by the control module but there is no control module between the high stop light and the fuse, just a relay contact fed by fuse 14 rh heelboard. The relay coil is driven directly by the brake switch, not the controller.

 

So Al,

you state these two bulbs don't fit - I searched for 1996 xj6

Linky to bulbs

 

There are 9 different bulbs listed as potentially being compatible, so no I didn't test all 9 both for cost and especially because I could tell by looking that the multi-LED units would not physically fit into the reflector without drilling out the hole. The initial two versions shown in the link with 5 LEDs definitely will not fit, and I tested a set like those, maybe even exactly the same.

Most(all?) of these bulbs will not physically fit as-is because they are larger than the diameter of the 194/2825 incandescent bulb. Through experimentation I now know this is easy to quickly visually assess if the LED "bulb" part is much wider than the base of the 194/2825 bulb in any dimension. In the cases of the multi-LED lights the corners of the side LEDs will hit. And in the cases where I tested some single LED bulbs, they too were slightly too wide as they often had a "ring" around them that was larger than a standard 194/2825 bulb.

The hole in the reflector through which the incandescent 194/2825 bulb fits is essentially/nearly exactly the same size as the glass bulb with very little room to spare. So if the LED is really any wider in any dimension, it isn't going to fit.

I had a few of these "no fit" types, probably still do in a drawer somewhere, but I hadn't ever electrically tested them because I hadn't drilled out the reflector to do so back then as I found the single LED (which I think I ground down to fit) I did electrically test at the time burned the fuse (and now the Sylvania/Osram single LED too) so I figured five or more LEDs might be even worse


I don't recall if I ordered these/which exact part numbers over a year ago when I first tested this, but I know I tested ones that looked exactly like some them such as the simple 5 LED (one top, four side) examples.

Although I now do have a reflector that is drilled out and could possibly fit any number of multi-LED alternatives, I'm not of the mind to go buy another $50 worth of multi-LEDs to test when the two single LEDs (again one from Sylvania/Osram) burns the fuse in two different 3rd light mountings.


This is the Sylvania/Osram I last tried:

http://b.cdnbrm.com/images/products/...194RLED_BP.jpg


Note that the following version looks a bit different and seems to be more slim, so it *might* physically fit, although I don't know if it is available in red. But then one would have to see if it doesn't pop the fuse:





But if someone else does want to continue testing and does find an LED that works, that would be great


.

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I have successfully installed 4 led bulbs into my high mounted brake light unit on my XJR.
Suitable led bulbs were obtained on E Bay. These bulbs measure 18mm x 10mm & are basically the same size as original. They have no problem passing through the opening on the light unit.
Next problem as experienced by Al, the led bulbs have the contact wires passing down both sides of each leg. The original bulbs have them staggered, positive facing one side & negative facing the other. Inspection of the bulb holders reveals that insertion of led bulbs with wiring covering both sides of the bulb leg results in positive wire touching onto both positive & negative part of the bulb holder. The same occurs with the negative, thus a blown fuse.
To overcome this merely remove the wire from going down both sides leaving just the negative wire on one side & positive on the other same as the original bulbs. I actually bent the wires out sideways straight & then passed them through to the respective lugs on the bulb holder as explained later.
Other important aspects are -
: Led bulbs are usually polarity sensitive ( unless canbus spec) & you must establish the positive & negative wire. The bulbs I purchased were marked.
:The negative track on the brake light unit is on the bottom side so when inserting bulbs you must ensure negative wire goes to the bulb holder lug touching on this track.
:I found the single thin wire did not make good contact with the bulb holder fittings so actually inserted the bulbs with the respective wires running up & onto the connecting lugs that touch on the respective track. A small dab of solder secured each wire in place.
I marked the bulb holders to indicate the negative lug & when inserting into the unit, ensure all 4 bulb negatives are touching on the negative track.
Pictures attached show led bulbs inserted in bulb holders prior to installation.

John Herbert (1996 Jaguar XJR)

 

Excellent discovery John! I didn't think to look into the special bulb holder to see that it allowed for the short in that scenario. That solves the shorting issue.



Thanks for the putting the effort into running this down and figuring out the trick needed to get this to work. Clearly Jaguar and Hella didn't foresee bulbs with a sightly different base wiring design, one that is now more the norm with LEDs replacing the original incandescent versions they were designed to use.

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