Jaguar XJ-S. Manual - part 148

 
 

587

“But the OEM fusebox has five fuses.”  Well, you can use one of these 4-fuse blocks and add a separate inline fuse.  A 
better idea, though, is to install two blocks and use the extra fuse locations as places to hold spare fuses -- or replace 
some of the inline fuses in the car such as the one to the radio or the one to the A/C compressor. 

When done, be sure to use your computer to slap together a chart of your new fuse locations, print it out so it looks 
professional, and install it adjacent to the new fuse block for future reference. 

 

ADDING INLINE FUSES:  In the author’s ’83, the inline fuses consist of a little tubular plastic container with a wire 
in each end; when the two halves are twisted apart they reveal a glass tube fuse within, with a spring providing contact. 
 These work OK -- but there’s certainly no reason to use inline fuse holders of that type any more.  Some modern 
Japanese cars use a type of plastic fuse called a JCAS fuse.  A JCAS fuse is a little plastic box with a clear window on 
the top for viewing the condition of the fusible link and a pair of 1/4” female spade terminals in the bottom.  So all you 
need to do is attach 1/4” male spade terminals to the ends of your wires, plug them into one of these fuses, and you 
have an excellent inline fuse arrangement. 

JCAS fuses are available in 20A, 30A, 40A, 50A, and 60A ratings.  They don’t seem to be available in anything 
smaller than a 20A, but that usually isn’t a problem; any serious short will blow a 20A before toasting any wiring, even 
fairly small wiring. 

 

 

Instrument Panel

 

 

The illumination of the instrument panel is discussed on page 634. 

 

VERTICAL VS. ROUND GAUGES:  Earlier XJ-S dashboards have four small gauges that are rectangular and the 
needle moves vertically.  When the bodywork was revamped in 1991, however, Jaguar went with a revised dash with 
all round gauges.  According to Alan Akeister, “There is a company in the UK, however, who can convert older models 
to dials.  They are called Autostyle Ltd.”  See page 711. 

Unless stated otherwise, most of the tips that follow refer to the earlier style instrument cluster with four small vertical 
gauges. 

 

INSTRUMENT PANEL REMOVAL:  Section 88.20.01 of the ROM and Chapter 10, Section 69 of the Haynes manual 
describe how to get the instrument panel out.  Note that both say you need to remove the underscuttle casing on the 
driver’s side, but this really isn’t necessary unless you drop something.  Both manuals also mention having to 
disconnect the speedometer cable from the right angle drive, but they must be talking about early cars -- the ’83 has an 
electronic speedometer, there is no cable. 

 

INSTRUMENT CLUSTER SNAP-ON COVERS:  At each end of the row of warning lights is a snap-on cover that 
hides the screws that hold the warning light lens assembly as well as the screws holding the entire instrument cluster in 
place.  On this author’s ’83, these covers had distorted with age and lost their snappage, so they loosely rattled around 
in the openings.  Shipping crates are often banded shut with 1/2” wide straps made of really hard steel, almost like 
spring steel; I cut a piece of that strapping about 2” long, bent it up 90º at each end, trimmed it a little to fit and inserted 
it between the retention prongs on the snap-on cover.  The metal thus provided a backing spring pressing the plastic 
prongs back out to their original positions, restoring the snappage.  Since I cut the ends just short enough that they 
didn’t quite reach the end of the plastic prongs, the sharp edge of the steel dug into the plastic a little so the tension held 
the metal piece itself in place -- although it wouldn’t be hard to add some double-sided foam tape between the center 

 
 

588

section of the steel and the back surface of the cover to make sure it doesn’t go anywhere.  My covers now hold 
themselves firmly and properly to the dash. 

 

GROUNDS FOR COMPLAINT:  There is only one ground wire to the instrument cluster; it’s the contact on the 
smaller of the two harness connectors that is separated from the rest by an omitted contact.  This single contact provides 
the ground connection for everything on the cluster -- gauges, indicator lights, illumination lights. 

If you’ll trace the conductor from the socket, you’ll find that about an inch away it becomes a very narrow conductor 
indeed.  Without having done any analysis of the load carrying capacity of that section of copper foil, let’s just say that 
having all the 2.2W dash illumination lights on might result in a measurable voltage drop in this area -- which would 
screw up the gauge readings. 

The fix is easy: provide an additional ground.  Pick one of the several other screws on the flexible circuit that makes a 
ground connection, and attach a wire to it and connect it to ground behind the dash.  Use of a spade connector will 
allow the instrument cluster to be removed and installed easily as before. 

 

Instruments and Gauges 

 

FLAKY INSTRUMENTS:  There are four vertical gauges in the center of the instrument panel on most older XJ-S’s, 
and they are unreliable -- not because they quit working altogether, but because they never seem to provide consistent 
readings.  Brian W. Rice writes:  “All gauges in my 85 XJ-S read low by 25% when I acquired the car several years 
ago.  I did some tests by lifting No. 4 fuse and applying a variable voltage to the dead end from a power supply, making 
sure not to exceed 15 volts.  With precisely 12 volts applied the voltmeter showed about 9V.  The fuel gauge also only 
indicated 3/4 with a full tank of petrol.”  These problems are because the wiring to these gauges is a disaster, with at 
least four likely locations for poor connections on each lead to each gauge. 

Even if you don’t think you have a problem with the gauges, it is suggested you do a minor overhaul and cleanup of the 
instrument cluster anyway.  It’s really easy, anyone can do it, and it’ll only take a couple hours even if you’re really 
milkin’ the job. 

First, remove the instrument cluster from the dash -- see notes above.  Second, remove five screws from the back side 
and separate the front cover from the rear housing of the instrument cluster.  This will give you access to all the innards. 

Now, if you have a VOM, you should be using it.  Check the ohmage of each circuit from the socket where the wiring 
harness plugs in all the way to the brass nuts on the screw posts on the side of the gauge itself.  Of course, these circuits 
should read zero ohms, or maybe some really small amount like 0.1Ω if you have a sensitive digital VOM.  Basically, 
they should read pretty much the same thing you read if you just connect the leads of the VOM together. 

You’re likely to find some poor connections indeed.  This author found circuits with more than 2Ω.  That may not 
sound like much, but it’s a lot for a circuit that isn’t supposed to have any measurable resistance.  Of course, if you 
don’t have a VOM, just dive in and fix all the connections described below as though they are all bad. 

The first likely source of trouble is the harness connectors themselves.  The entire panel is wired with a clever flexible 
printed circuit, and the harness sockets are formed by folding portions of this flexible circuit into a hole and pushing the 
plugs in; the connections on the sides of the plug make contact with the bare copper on the flexible sheet.  There’s not a 
whole lot you can do here other than clean up the connections a bit (rub with fine sandpaper or the like) and perhaps 
apply some Ox-Gard to prevent further corrosion, but if some of the circuits are really messed up, here’s a tip: places 
that do stained glass work use thin copper foil tape, and some of this tape might be usable to fix a damaged connection 
on that flexible circuit.  Another idea is a hobby shop; places that sell stuff for model trains and the like sometimes sell 
copper foil conductors for sticking down on a surface and then painting over so there are no wires visible. 

Each of the four vertical gauges is connected to the flexible circuit with screws with stainless steel wavy washers under 
the heads.  Here’s the second likely spot for a bad connection.  If you’re in a hurry, you might just loosen the screws a 
bit and retighten, since that will usually make a good connection for a while.  For a more permanent solution, there are 

 
 

589

several suggestions.  Besides polishing up the copper surface, you might consider replacing that wavy washer with 
something with a little more “bite”.  Basic steel is not recommended, though; this is one place you don’t need rust.  
Some hardware stores sell bronze lock washers; if you find some in a suitable size, they’d probably work well.  You’ll 
need at least 29 of them.  Alternatively, you might just take a pair of pliers to those wavy washers and make them more 
wavy.  Rice makes another suggestion:  “I was able to repair by soldering tinned copper wire to the flexible circuit 
board tracks being careful not to melt the plastic flexible board and fashioning the wire into circular washers to go 
under the terminal nuts thus establishing good contacts again.”  If you try this, you might want to go to the effort of 
removing the entire flexible circuit from the cluster so you can solder on it separately, avoiding the possibility of 
melting the plastic housing itself. 

If you have trouble getting either of these first two type connections working reliably, you could just get PO’d, yank the 
entire flexible circuit and throw it away, and wire the entire cluster with wires with loop connectors and the like.  Your 
biggest problem will probably be making connections to light bulbs -- and there are a lot of connections to light bulbs!  
You might consider applying a small strip of that copper foil tape on each side of each socket and install a self-tapping 
screw through it into the plastic to attach your wires to.  You can dyke off the plugs on the harnesses and install generic 
Molex connectors to connect to your wires. 

The screws for the gauges appear to simply screw into a tapped hole in the plastic housing.  How can that make an 
electrical connection?  Looking at the other side, each gauge is mounted on a small printed circuit board (this one’s 
rigid) with three broad copper conductors.  This PCB fits into a slot and is held in place with two small clips.  When the 
screws are threaded in from the back side, the threads dig into the copper conductors on the face of this PCB -- that’s 
correct, the third likely place for a bad connection.  Of course, one possible fix here is to use a longer screw so it screws 
farther up the side of that PCB and contacts it with more threads; again, a screw that’s likely to rust is not 
recommended, brass screws might be a good idea. 

Remove the two or three connection screws and two clips on a gauge and lift it out.  You will note that the gauge is 
mounted to the little PCB with three brass nuts and wavy stainless steel washers.  This is likely bad connection number 
four; it may not appear as likely to cause trouble as the first three, but in fact on this author’s car these nuts were the 
worst problem! 

The fix for the last two types of bad connection is one operation.  Remove the three brass nuts and separate the PCB 
from the gauge itself, being careful not to drop the small panel behind the PCB or a mysterious clip around one post 
that seems to do nothing but provide proper spacing.  Set the gauge aside; if it’s been working at all, it’s not likely 
there’s anything wrong with it.  Polish both ends of each conductor on the PCB, then set it down on a flat surface and 
apply some solder.  It solders really well.  Build up a ring of “tinning” around each post hole, and tin an area at the end 
of each conductor for those screws to dig into.  When cool, wipe away any excess resin and reassemble.  You can easily 
do one gauge at a time so you don’t mix anything up. 

 

GAUGE REPAIR:  All four vertical gauges are of similar design: two stationary coils at 90º to each other, and a 
heavily damped rotor.  Automobiles have always used damped gauges; not only does it reduce the likelihood of damage 
from vibrations in the car, but gauges zipping up and down make drivers nervous. 

Val Danilov reports, “Once I was sure that the oil gauge was faulty and not the sending unit, I pulled the gauge out of 
its housing by removing 3 screws from the back of the plate the gauge was attached to, as well as 2 metal clips.  It’s 
pretty much self-explanatory once you get to it.  Once the gauge was out, in good lighting, you can see several hair-thin 
metal wires that run from the winding to 3 metal posts on the periphery of the gauge.  The wires are soldered to the 
posts in such a way that they appear to be misplaced (as if they should extend farther to some other point), when in fact 
they are simply so small that you cannot easily see the points of attachment.  When trying to move them with a tiny 
screwdriver, I found one wire which was loose.  I used a regular soldering iron to affix the wire back on the post.  
Voilà! Problem solved. 

“When the gauge is out of the instrument cluster, it is very easy to test it with a 12 volt supply by simply connecting one 
of the electrodes to +, while grounding the other electrode.  Note: the gauge has 3 electrodes (nuts on the threaded ends 
of the posts), do not use the middle post.  The post nearest the bottom of the gauge is ground.” 

 
 

590

 

85 MPH SPEEDOMETER:  Regarding why some XJ-S’s came with 85 mph speedometers, Randy K. Wilson says, “It 
affected 80, 81 and 82.  It may also have been in during 83... not sure.”  This author’s ’83 has a normal speedometer -- 
but perhaps it was retrofitted. 

David Berman adds, “It resulted from a regulation from the US National Highway Transportation Safety 
Administration (NHTSA) during the leadership of "safety-czar" Joan Claybrook, during the regulation-happy Carter 
administration.  The purpose was to prevent kids from being enticed by the "century" mark.  It was effective for the 
1980 model year. 

“The regulation was thankfully scrapped in 1983 as part of a regulation-reduction program of the first Reagan 
administration.  Most non-US vehicles returned to "real" speedometers for the 1984 model year, but US manufacturers 
retained the 85 mph speedos, at least for their high-volume car lines, for a very long time.” 

If you don’t like the 85 mph speedometer, it can simply be replaced with a normal speedometer from a different year.  
John Napoli says, “I did this on my car about a year ago.  Bought a 160 mph unit from a junkyard.  Installed easily and 
works great.”  Of course, the replacement speedometer will likely have a different odometer reading, and you’ll just 
have to deal with that. 

 

INTERMITTENT SPEEDOMETER:  Several owners have reported on electronic speedometers that work sometimes, 
other times they sit at 0.  Robert Louis Woodling says, “If the wires sag on the exhaust the insulation melts and the 
speedo stops working.  The intermittent symptoms could be the beginning of insulation meltdown or a poor 
connection.” 

 

SPEEDOMETER/CRUISE CONTROL/TRIP COMPUTER/SERVICE INTERVAL COUNTER SIGNAL:  That’s 
right, the speed signal goes to as many as four separate places.  This signal got to its destination by at least three 
different methods over the life of the XJ-S.  The early cars had cable-driven speedometers and service interval counters; 
a cable came off a small angle gearbox on the side of the transmission, went to the service interval counter, and another 
cable went from there to the speedometer.  Walter Acker IV says, “On my ’76 XJ-S the cable driven service interval 
counter is behind the dashboard in the area of the radio.”  The cruise control had its own sensor on the front end of the 
drive shaft.  Of course, there was no trip computer on these early cars. 

The angle gearbox was apparently customized to utilize the same components with the GM400 that had been developed 
for use with the BW12; it not only provides a ratio change, but it also converts to a different type speedometer cable -- 
the threaded coupling is different, and the size of the squared section on the end of the cable itself is different. 

Early 80’s cars switched to an electronic speedometer that got its signal from a pulse generator that mounted on the 
very same angle gearbox.  The mechanical service interval counter under the dash was replaced with an electronic 
service interval counter located to the trunk.  The cruise control was altered to utilize the same signal, eliminating the 
need for its own sensor.  The two wires that connect to the pulse generator are 12V power and signal. 

The pulse generator changed part number in 1984 with the introduction of the trip computer.  Ron Whiston says the 
differences are obvious, the color is different, the plug is different, but the dealer may still hand you the wrong one.  It’s 
best to take the old one with you when buying a replacement. 

Peter Morris provides some suggested tests for this sending unit:  “Check the transducer by getting under the car and 
pulling the unit, spinning the drive while someone verifies speedometer movement.  This is not a conclusive test, 
however.  If the there is no movement, another check, also performed under the car, is to disconnect the transducer, and 
connect a pair of clip-leads to the chassis-side connections.  Clip one clip-lead to a heavy screwdriver and the other to a 
file.  Drag the screwdriver across the file while someone watches the speedo.  If there is speedometer indicator 
movement, then you can reasonably assume the wiring and connections to the speedo (and trip computer) are good.  
The next logical step would be to replace the transducer.”