So i worked on the number plate light’s changed the inline fuse’s but still one light wont work i changed sided with this relay (!!!) And i figure that this doesnt work…
What does it do and where can i buy replace o e ?
It’s the little box that detects if you have a failed light.
When I had one that failed I took a replacement from a parts car.
Its very hard to find a replacement car in israel 
Mybe one of the guys here could help with that…
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Someone smarter than me might be able to tell you how to rebuild one of those as the circuitry can’t be that complicated. You can also bypass it, which would get the light working again.
This came up a few years back. Really bad design to have failure of the failure module default to inoperative lights. It should be designed so that failure allows the lights to work if they’re going to, and of course not work if, coincidentally, they fail at the same time that the module fails. It’s like designing a defibrillator to cause a heart attack when its battery runs low.
Unplug the red wire and the red/orange wire from the bulb failure unit, and join them together with a jumper. Ignore the white wire. The tail light/number plate light should work.
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O.k thank you i’ll try this
That’s not what should happen. The lights should be operative no matter what. The only thing that should go wrong with this sensor is flaky operation of the warning light on the dash.
I don’t even know how it’d kill the lights. Probably time to pry it open and see what’s what.
So i open the part and this is what i found inside…
I see that one end of the wire is not connected to the plate.
Kirby, I had the exact same failure on my black XJ-S back in college - and it was something we came across at the shop fairly regularly. So whether or not it should happen, it’s a common failure mode.
Shahar, Your bulb failure unit has burnt out. The coil of resistance wire carries the current to illuminate the tail lamp, and as the wire heats up, it causes the bi-metal strip to bend, opening the contacts, and allowing the warning light on the dash to go out. You might as well give up on the idea of repairing the unit.
If you cannot live without a bulb failure unit, they are still available, but rather expensive, considering what they do.
The part no is DAC 1910. Normal suppliers here in the States.
Out of interest I’d be tempted to measure the wire resistance and see if I could replace the small coil with a home made replacement…maybe some fuse wire …be cheap and easy to try…??
There are at least three different versions of the Bulb Failure Units that I am aware of that are common between some different models of Jaguars. The first is Jaguar part number DAC1908 (LUCAS LFS 1002/03) that has a green dot on it. The second is DAC1909 (LUCAS LFS 1002/02) that has a blue dot on it. The third is DAC1910 (LUCAS 1002/01) that has a red dot on it. I have a small box of them that I harvested from my three Series III XJ6 parts cars because they use all three kinds. All three kinds are shown in the two attached pictures.
I contacted Shahar via PM about this.
If anyone else wants to purchase any known good and tested ones for $10 each plus shipping just send me a PM. I have four green, 6 red, and 10 blue ones on the table in front of me and possibly a few more of each in boxes in my garage. I will test them in my 1984 XJ6 Vanden Plas before shipping them to make sure that they are still good before shipping them out.
Paul
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If you want to build something, I pondered fabbing something using a NC magnetic switch such as this one:
https://www.newark.com/littelfuse/59025-040/magnetic-sensor/dp/05M4563?st=spst-nc
I’d wrap a little coil, perhaps around it, perhaps around something attached to the end of it, in such a way that when current passes through the coil it opens the switch. Then I’d experiment with the number of turns on the coil such that it just barely opens the switch, so when one bulb burns out it doesn’t open the switch. Easy peasy and cheap, and it has the advantage that it works instantly, you don’t have to wait 30 seconds for the bulb failure warning light to go out. Plus there’d be far less resistance in the circuit to the bulbs, so they would burn brighter.
Nichrome wire is easy to come by. You can just steal some out of a toaster.
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…just don’t tell the wife.
If I were making a replacement I would go electronic. A simple OP AMP based comparator circuit would do it. I did something similar with my Alfa’s fuel gauge. I’d already added an anti-slosh circuit, but then the low level connection on the variable resistor coil failed so I used a LM358 comparator to monitor the level and turn the low level warning light on. This allows you to preset the trigger value. For the failed bulb scenario this would allow you to fit LED bulbs and still be able to monitor their operation.
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Bravo! Yes, exactly so. Finally an engineer doing upgrades to systems and parts that is actually a simple more functional and better part as well as being an upgrade.
Paul
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Kirby: that reed switch is an interesting device. Price is sure enticing.
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Select an older tin type dead relay. Steal the wire from the coil. Wrap the same length in the warning lamp sensor. probably close enough to0 function.
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Fusible link wire? The after market custom harness on my lump has two!! So far so good, but, I’d prefer another means of protection. Big visible blade fuse or ??
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Were it my car, I’d consider just “jumping” the device and rely on visible inspection. Although my jeep has some means of lamp fail detector, son and I did the visual. It’s display panel show which lamp is out! It did that a few years ago. A license plate illuminator!! The thing even fusses about low WS washer fluid!!!
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Not sure which years. But Chevrolets warned of no tail lamps by having the dash light fail to light up…
Carl
Several years ago, I had the idea to redesign the Smiths bulb sensors to accommodate LEDs. My design used an LM7301 comparator. The circuit was simple, but the mechanical fabrication of an electronic enclosure to have the same form and fit as the little metal can became complex. Given the reliability of LEDs, I finally decided to just bypass the bulb sensor and leave the metal cans in place. BTW there is a significant voltage drop across those sensors; bypassing them will noticeably increase the brightness of your bulbs, esp LEDs.
Ron