This post is for anybody thinking of upgrading bulbs, especially interior, with LEDs.

When I bought my 2002 XJ8 it was in very good condition, but more than half of the interior bulbs had burned out and had not been replaced. I decided to replace the bulbs with LED bulbs primarily because they would not burn out and require me to replace them. I also replaced the exterior lights including the headlights. I am an electrical engineer and all-around tinkerer so much of this is a lot more work than many of you would care to do, but here is a summary of what I learned for anybody who might be considering a similar upgrade to LEDs.

You may want to stick with incandescent/halogen
For purists, you may want to do this anyway.
The stock bulbs draw about 10 times the power/current as LEDs. The interior LEDs are also generally brighter so if you do not replace them all there will be a noticeable difference in intensity.
Many of the Jaguar's circuits were designed to expect the higher current draw of incandescent bulbs and you will need to add additional components to get correct functionality,

• Reverse and brake lights will need an additional high-wattage resistor in parallel or else the instrument cluster will flash a warning that your bulbs are burnt out. Similar problems with the turn signal lights blinking too fast. This is a common and well documented problem you can find information about on the internet.
• Three bulbs in the instrument panel flickered during warm weather: the odometer and the two headlight indicator bulbs (high-beam and low-beam). At first I thought it was the instrument cluster and tried replacing the whole instrument cluster but there was still flickering. I ultimately went back to halogen bulbs for these three bulbs and the flickering went away.

Other problems
It is difficult to find direct replacements for the interior bulbs which come with the plastic sockets. I had to buy other automotive LEDs and then remove the wires to re-wire them in the existing sockets which I salvaged. Ultimately I ended up just soldering many of the LEDs directly onto the circuit board as this proved to be more reliable. After 15+ years the salvaged plastic sockets were often degraded and brittle.

You have to worry about polarity with LEDs. Plugged in one way they work but not reversed. This took a bit of trial and error. I may publish some photos showing the polarity I figured out.

Color matching is a problem. The stock color looks to be blue-green and I found bright green and bright blue LEDs. I went with green but I am not totally happy with the results. I experimented with covering the green LEDs with a little semi-transparent blue paint and was happy with the color and it also reduced the intensity to more closely match the original bulbs. But there was a lot of variation in the thickness of blue paint I applied so the intensity varied a bit. So I just went with the basic green LEDs.

If I had to do it all over
In general I am happy with the upgrade of 90% of the lights. For the odometer and the high-beam and low-beam lights, just stick with halogen. The reverse and brake lights I still like LED, but I want to find the exact resistor value that would work so that the detection circuitry would still detect when a bulb is not working. This may take some trial and error. Replacement of headlights with LEDs is very good and I have much brighter and whiter colors.
To solve the blue-green color and intensity problem for interior lights I plan to experiment with some blue plastic film over the green LEDs. Buying a film should give me the consistency I was missing with the blue paint.

 

FYI : They make "canbus error free" LEDs now w/ the resistor built in.

 

Thanks for the info. I did a full led exterior lighting on my previous x308. It would only blink fast on the inside. Outside was normal.

 

As KC says, CANBUS are readily available and I've posted such.... superbrightleds.com has many of both readily available and in different colors. They are quick to respond if you have a Q and are plug and play for the most part. Plugs like blinkers and such may still require load resistors inline.

My dash and 3rd brake light are LED and I found out that the CANs are needed for the dash because of the dimming function. There are many threads on this from way back in 2009 from folks who were soldering resistors onto the LED's before CANBUS.