Here is a modification that I made to my wife’s 1990 XJ-S convertible in response to her concerns that the instruments were difficult for her to read at night. I also had the same problem with the odometer and trip odometers. In my first attempt to fix this I removed the instrument panel from the car, removed all of the green plastic bulb covers, cleaned the bulb contacts, cleaned the main connector contacts, and then reinstalled the instrument panel. She said that this helped a bit, but said that some of the instruments were still hard for her to read. They were also difficult for me to read. In my second attempt I bypassed the instrument panel lighting rheostat on the dashboard with a jumper plug that I made from a connector that I harvested from one of my XJ6 parts cars and provided full lighting to the instrument panel. The attached pictures show what I did with the jumper plug and how the instrument panel looks now. She told me that she no longer has problems reading the instruments at night, and neither do I. We have been driving the car at night and evaluating the lighting for a while and it has worked out very nicely. Please let me know if you have any questions.
Regards,
Paul M. Novak
1990 Series III V12 Vanden Plas
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA USA
I’ve often found that bypassing the rheostat gives the improvement I was looking for.
On my present Series III I’ve joined the bandwagon and used LED bulbs…but it hasn’t been entirely successful. Getting the tach and speedo the same brightness as the other gauges is problematic…and more annoying than the dimness issue.
I may go back to the standard issue bulbs with a bypassed rheostat
Thanks for the feedback. I was evaluating different ways of improving the lighting and probably would have considered the LED route if this didn’t work out. As it is my wife is happy with the improved lighting at night, and so there is no need for me to consider anything more. I like to keep our Jaguars as original as possible, but I have made modifications to most of them to improve reliability or ease of use. The jumper plug approach appealed to me because once I figured out how to do it, the car can be returned to the original configuration within a minute or two by dropping the under scuttle panel, removing the jumper plug and reconnecting the rheostat plug because I didn’t make any permanent changes to the wiring. In some of my other modifications (like the added window switches to control the rear windows) I did have to solder in some new wires and modify other things to get it right. But the jumper plug was easy to add and remove if needed.
I do not have the same “originality” bug as you Paul, although if it pleases you why not ?
Jaguar engineers of the 1970s to 1990s designing the XJ-S would have a field day if they could use all the new generation of gadgets. If by some miracle all the XJ-Ss still around could go back through the factory and be updated they would come out the other side with a lot of changes under the skin, and mostly for the better. One exception being the over elaborate door locking & anti-theft systems that still baffle me in my XJ350.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
5
If that’s true, I think something’s wrong with the rheostat! Turned to full
brightness, it should simulate a dead short. That means there must be a
poor connection in there somewhere.
I never delved any further into one than cleaning with electrical contact cleaner…under the presumption that the track and wiper might be gunky. No help. It’s just too easy to bypass it and call it good !
You are probably correct about something being wrong with the rheostat. The rheostat in this car was a little flaky since we got it and the brightness varied up and down unpredictably while rotating the knob. This car spent a lot of time in Florida before I got it and there have been some other minor corrosion issues with electrical components primarily. I asked my wife if she thought I fixed the instrument panel lighting after I disconnected the rheostat and installed the jumper. She said that it was fixed since she could now read the instruments at night and it didn’t matter to her that she couldn’t dim the lights with the rheostat. So, much like Doug I moved onto other projects. That was a year or two ago and since it seemed to be a successful modification, I decided to post my results for others to consider. Instrument panel lighting issues come up from time to time on this list and I thought that others should know that when I removed all the green lamp covers and installed a jumper to bypass the rheostat, that problem was solved in my wife’s 1990 XJ-S convertible.
I had the exact same problem, so I took the rheostat apart.
What I found was that the rotating arm was not going all the way to end, so it always had some resistance.
I removed the excess piece of the wire coil and soldered in its place a thin brass plate.
Now at full brightness the resistance is 0.
Made a noticeable difference at the instrument lights and still have the dimming option.
Rob,
I soldered all three wires in my jumper plug together and used shrink tubing to protect the soldered wires. There are three wires in the original car harness. One was Red-Blue (RU), and two were Red-White (RW). The RU wire normally provides the 12VDC from Main Fuse #7 to the rheostat and the RW wires deliver the modulated voltage to the variety of instrument panel, center panel switches, and the cigar lighter, gear selector, and fiber optic lamps. When I made and installed my jumper plug, and disconnected the rheostat, I connected the RU wire directly to both RW wires bypassing the rheostat providing the full voltage to all the lamps on the panel light circuit. This was quick and easy for me to do with parts that I harvested from my Jaguar parts cars, made no permanent change to the car wiring, and is easily reversible should I ever decide to figure out what is wrong with my rheostat or replace it. For now the lights are nice and bright and easy to read at night. The one drawback is they are not adjustable. My wife likes the panel lights bright at night and she is happy with how easily she can read the instruments at night. So, I will likely leave her car this way as I continue the cars restoration.
Thanks Paul… I guess 89 and 90 are different animals. I went to work on
mine yesterday and found a different set up. Three separate plugs on the
rheostat. Thanks to my parts car I had another rheostat the worked so all
works now.
Thanks again.
Rob
