What is a good replacement bulb for the old dash/instrument lights???
Dim instrument panel lights is a common complaint among prefacelift XJ-S owners and you will find a lot of posts about this in the archives. I think some have replaced the original bulbs with LEDs, but I can’t speak to that modification.
I fixed this problem in my wife’s 1990 XJ-S convertible in two steps. In the first step I removed the instrument panel and partially disassembled it to remove the green plastic lenses over the bulbs that discolored to brown with age, reassembled the instrument panel and reinstalled it. My wife was pleased with this improvement but asked if I could make them even brighter.
In the second step I made a jumper plug and completely bypassed the dash light rheostat and this made a big difference. The original dash lights are now nice and bright white and I did not change the bulbs. I thought that bypassing the rheostat shouldn’t make a difference, but it sure did when I tested my jumper plug. Perhaps the rheostat was bad? The only disadvantage to this modification is that there is no way to adjust the dash light brightness, but that is no problem for us since we both like the nice bright dash lights now. I did not install any new bulbs.
So this modification worked out nicely, my wife is happy, and except for my time this didn’t cost anything to implement.
I broke off the green plastics that give the little bulbs their color, and replaced bulbs with bright blue LEDs. Nice and bright! let me know if you need part number. LEDs were $4 each.
The rheostat is the actual problem indeed.
In my XJ, same set-up, I discovered that the rheostat arm was never reaching the end of it’s travel, and never had zero resistance. I soldered a little plate to extend the direct contact between the arm and the base.
The difference in light was day and night and I still have a functioning rheostat.
Led conversion kits are available https://www.bettercarlighting.co.uk/index.php?searchStr=XJS&act=viewCat&Submit=Go
Thanks Paul! I have been planning to try this (bypass rheostat) for a long time, wasn’t sure that it would have any affect. Glad to hear that it seems to make an improvement!
Bypassing the rheostat made a big improvement in the instrument panel lighting in my wife’s 1990 XJ-S convertible but as Aristides points out it very well could be that we had a faulty rheostat. The instrument panel lights are nice and bright white, my wife is happy, and I have many other projects to do so this is my solution to to dim instrument panel lights.
Attached are some pictures of the jumper plug that I made using a similar plug that I harvested from one of my 3 Series III XJ6 parts cars, soldered the wires together and covered with shrink tubing. I first tried out my rheostat bypass idea using generic jumper leads and the improvement was so good that I created the permanent jumper plug. I also attached a tag to the plug to document this change for someone in the future who might wonder why the rheostat doesn’t work.
BTW, if you or anyone else reading this would like a jumper plug just send me a PM and i will see if I have any more. I already sold a few to others who read my posts in the archives and contacted me, but I am certain that I have several more of these connectors in the harnesses that I removed from my parts cars.
Once the jumper plug is made it is a simple matter of disconnecting the connector leading to the rheostat under the dash and plugging in the jumper plug.
That is interesting about your XJ saloon. This dash lighting modification was so successful in my wife’s 1990 XJ-S convertible that I made the same modification in my Series III V12 Vanden Plas because I found those lights too dim even with the rheostat turned to full bright. After bypassing that rheostat I have nice bright instrument panel lights in that car as well but no dimming capabilities, which is fine for me.
I have some spare XJ rheostats from my parts cars and maybe I will play around with them in the future to see if I can do something like you did.
That polarized plug is same as used on the cruise bellows; when I needed one of those, I just bought a “4 flat” trailer harness and cut off the unused terminal. They are only a few bucks at any auto parts.