Jaguar XJ-S. Manual - part 150

 
 

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Figure 29 - Bracket for Mitsubishi Reservoir 

If the MicroSoft gods are smiling down on us today, Figure 29 will print in actual size.  So, just load a piece of sheet 
metal into the ol’ inkjet and let ‘er rip! 

The bottom of the reservoir should be flush with the top of the existing support bracket, but the hose clamp will need to 
go around the reservoir about 1/2” up from the bottom; hence the two “legs” on this bracket being 1” tall.  There is even 
a little ridge on the Mitsubishi reservoir -- it’s actually the “MIN” level line -- that will neatly sit on top of one of these 
legs so it cannot slide downward. 

The asymmetric design of this bracket serves to mount the Mitsubishi reservoir about 1/2” closer to the power brake 
booster than the original reservoir was.  This provides more clearance to the throttle cable, as well as making it a bit 
easier to wrap your hand around the cap when unscrewing it. 

The bent-down tab at the lower left in the diagram is simply to provide a place to fasten the wire connector down.  If 
you wish, you can omit this tab and just slice the bracket straight across the bottom edge, and provide other means of 
fastening down the connector -- or just let it dangle.  A generic strip of steel with 1/4” holes can be used by merely 
bending it 90° in the middle and mounting it under the same mounting bolt that holds the reservoir bracket itself. 

The design shown above is for a LHD car.  Those with RHD cars will probably need to make a mirror image of this 
bracket -- which means cut out the exact same piece, but bend the two mounting tabs down instead of up and the wire 
connector tab up instead of down. 

The hose fittings on the Mitsubishi reservoir are 10mm, while the fittings on the Jag master cylinder are 1/4”.  You will 
need to devise a way to connect these sizes up.  A 3/8” air hose will fit the Mitsubishi reservoir just fine.  The simplest 
idea is to use two different sizes of hose with an adapter in between. 

 
 

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Another idea would be to take a short section of 1/4” red air hose and peel the red outer layer off, slide the black inner 
layer over the 1/4” fittings, slide the 3/8” hose over that, and clamp. 

Another solution might be to purchase some 5/16” OD steel tubing and some 3/8” OD steel tubing, both of which are 
available at auto parts stores as pre-made fuel lines.  Cut two 3/4” long sections from each.  Slide a short piece of 5/16” 
tubing over the reservoir end of each one of the 1/4” metal tubes used to connect the OEM reservoir to the master 
cylinder, slide a short piece of 3/8” tubing over the piece of 5/16” tubing, and braze or silver solder both pieces in place. 
 Then you can connect the metal tube to the Mitsubishi reservoir with short pieces of 3/8” hose, and you can connect 
the other end to the master cylinder exactly the way they were before.  Be sure to check the braze jobs for leaks before 
installing. 

Yet another idea would be to obtain a set of the plastic elbows that fit the Mitsubishi master cylinder and find a way to 
fit them to the Jaguar master cylinder.  The elbows actually appear remarkably similar except for the fitting size and the 
fact that the Mitsubishi parts have a tab through which a Phillips screw is installed to make sure they don’t go 
anywhere.  There’s no way to use that screw idea on the Jag, so the tab can either be cut off the elbow or just left there 
to hang off the side doing nothing. 

The Mitsubishi cap is clearly marked to use DOT-3 only or DOT-3 or DOT-4 fluid only, plus some stuff in Japanese.  
If you wish, you can cut those markings off -- they are raised letters on a flat surface.  Then you can print out a circular 
label with directions to use DOT 4 only along with a Jaguar leaping cat on a piece of peel-and-stick label material 
loaded into your inkjet, cut it out, and stick it down on top of this surface. 

Connecting up the wires for the switch is not a big challenge.  If you dyke off the connector from the Mitsubishi 
harness in the junkyard, you can just splice it onto the Jaguar harness (cutting off the spade terminals).  Many junkyards 
don’t like you cutting harnesses, though.  Still, this T-shaped connector must be a common shape, because many people 
manage to find one that fits.  If you can’t, don’t fret -- the female spade connectors on the Jaguar harness will actually 
plug right to the Mitsubishi connector.  It doesn’t matter which wire is connected to which terminal. 

You can review this entire installation at 

 

http://www.jag-lovers.org/xj-s/book/BrakeFluidReservoirFix.html

 

Besides having a level switch that will actually work when you really need it to, there’s another nice benefit of this 
reservoir replacement.  The OEM Jaguar reservoir is vented by letting air into the fluid, but the Mitsubishi reservoir has 
a diaphragm in the cap.  As the fluid level drops, this diaphragm moves with it, maintaining separation between fluid 
and air.  As a result, the fluid will absorb much less air and moisture, and require bleeding less often. 

Also, installing a Mitsubishi reservoir will solve problems with the OEM reservoir cap cracking. 

 

MITSUBISHI RESERVOIR PROBLEMS:  Ain’t this a kick in the pants!  You go through the effort of replacing the 
OEM reservoir with the Mitsubishi, and find that it has problems too!  Fortunately, its problems are not life-threatening 
and are easily corrected. 

As mentioned above, the cap used on the Mitsubishi reservoir has a diaphragm built in to keep air away from the brake 
fluid.  On Mitsubishis made before 1992, the cap itself has three small tangs inside and the diaphragm has three mating 
notches around the outer edge to prevent the diaphragm from turning around inside the cap as you screw the cap on.  
Unfortunately, what actually happens is that the diaphragm distorts at the notches while tightening, gets cockeyed, and 
loses the seal.  Result: air is allowed into the brake fluid.  In other words, when this thing screws up, it vents the brake 
fluid reservoir the same piss-poor way the Jaguar reservoir was designed to! 

Mitsubishi’s solution was to redesign the cap and diaphragm, omitting the tangs and notches altogether.  Who cares if 
the diaphragm rotates a little while the cap is being tightened?  If you happen to find yourself with a reservoir with the 
old style distorted diaphragm, you can fix it by purchasing a new cap and diaphragm from your friendly Mitsubishi 
dealer -- but the two parts will cost as much as a new reservoir with cap and diaphragm!  If you wish, you can purchase 
just the diaphragm and carefully cut away the tangs inside your old cap.  The diaphragm part number is MB895813. 

 
 

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So, if you go scrounging in the junkyard for a Mitsubishi reservoir, you might want to check that the cap and 
diaphragm are the updated design without anti-rotation tangs around the edge.  There should be only one notch, for 
venting the space above the diaphragm. 

Interestingly, Mitsubishis have been sold in the US badged as Dodges -- and Dodge came up with their own redesign of 
that cap and diaphragm.  Walter Acker IV found a reservoir in a Mitsubishi-made Dodge D50 mini pickup truck with a 
two-piece diaphragm: a rubber diaphragm with a hard plastic rim that snaps onto it.  The hard plastic rim allows the cap 
to be screwed down on the diaphragm without distorting it.  It also makes it easier to unscrew the cap later.  Use of this 
diaphragm also requires a cap with no tangs in it. 

You can review this diaphragm issue at 

 

http://www.jag-lovers.org/xj-s/book/MitsubishiCapUpgrade.html

 

 

ALTERNATIVE MITSUBISHI RESERVOIR:  Walter Acker IV went on to discover yet another type reservoir that 
can be used to replace the pre-ABS reservoir in the XJ-S.  This one is also from a Mitsubishi, but from their pickup 
truck instead.  The reservoir is rectangular rather than round, and is smaller than the round one, but will still work fine.  
The cap is black rather than the white one found on the round reservoir, and the reservoir Acker found doesn’t have the 
problem with the tangs around the edge of the diaphragm -- but it’s unknown whether that’s simply because the one he 
found was a post-correction model or whether the pickup truck never had this design flaw in the first place.  It still has 
10mm fittings, so it will require the same hose adaptors described for the round reservoir above. 

 

BRAKE WARNING LIGHT:  Mike Morrin warns of another reason the brake warning light may seem to have failed 
in the “on” mode:  “When I got my car, the warning light was on, but the handbrake adjusters (on the rear calipers) 
were seized.  Fixing the adjusters put some extra tension on the cable, and the warning light switch then started 
working.” 

 

PARK LAMP FAILURE SENSORS:  There are park lamp failure sensors in the trunk up behind the lip on both sides, 
as well as under the right side dashboard.  The ©1982 Supplement says there is only one under the dash to serve the 
lights on the front of the car, but it lies; there are two, one serving the front right and one serving the front left.  They all 
look the same: a small metal box with three terminals.  The current to a light goes in one terminal and out another, 
heating up a conductor inside.  When it gets hot enough, a bimetal strip bends enough to break the third connection to 
the dash indicator.  This is why it takes a few seconds for the indicator to go out when you turn on the lights.  If a bulb 
burns out, the reduced current doesn’t heat the bimetal strip enough, so the indicator stays on. 

If your dash indicator is staying lit for unknown reasons, the first thing to do is check that all the lights on the car are of 
the correct wattage; a lower-current bulb can fool the sensors.  Then, find each sensor and disconnect the indicator 
wires (WS) one by one until you find which sensor is keeping the indicator on. 

If one of the sensors isn’t working right, they can be adjusted.  There is a tiny screw on the box near the terminals, 
sealed with a drop of glue.  When you’re absolutely sure all the bulbs are working right, leave the lights on for a couple 
minutes.  Turn the screw clockwise until the dash light comes on, then counterclockwise just until it turns off.  Be 
careful not to touch ground with the tool used to adjust the screw. 

An owner reports on a late model:  “My 94 XJS gave me a dashboard indication of a bulb out but going around and 
around the car, all lights seemed to be working.  This drove me nuts until I finally noticed the sexy little bulb that gives 
the headlight assemblies a little glow when the parking lights are on.  It was working on the driver's side but not the 
passenger side. I didn't know it was even there and it has to be dark out to see it.  Low and behold, I replaced the tiny 
bulb (standing on my head to do so) and all is well again.” 

The stoplamp failure sensor is different; see below. 

The indication that a turn signal bulb has failed is that the turn signal dash indicator just blinks once, or not at all, while 
the functional bulbs on the outside of the car continue to blink properly. 

 
 

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STOPLAMP FAILURE SENSOR:  The failure sensor on the brake lights works differently than the ones for the 
taillights because having the warning light come on for a few seconds every time you hit the brakes would be 
unacceptable.  A brake light bulb failure shows up on the same dash indicator, though.  With the ignition on, headlights 
off, handbrake applied, and the brake pedal pressed, the indicator should come on; if it does not, there’s a bad circuit or 
bulb in the brake lights. 

Colleen Melton says, “My '79 XJ-S recently had a mystifying, extremely aggravating problem.  At random, the fuse for 
the brake lights (15A, #5 in fuse panel) & turn signals would blow.  We isolated it down to the brake light circuit by 
deliberately not using the turn signals and waiting for the fuse to blow... At no regular interval, applying the brakes 
would cause the fuse to blow. 

“After examining all accessible wiring and the bulb sockets, my husband concluded the problem was likely in the brake 
warning relay, located in the center console under the rear portion of the ski slope.  He removed the 'relay' and opened it 
up.  Sure enough, a blob of solder on the brake light input wire (14 ga green/purple) terminal was touching against the 
steel case of the 'relay'.  Closer examination revealed the rivet holding the outer spade terminal to the inner solder 
terminal had loosened, allowing poor contact leading to high resistance producing heat, increasing resistance, leading to 
even more heat...  This apparently got bad enough that the solder connecting the coils of wire wrapped around two reed 
switches (one for each brake light output) got hot enough to melt somewhat.  In addition, a diode in the circuit was 
cooked by the heat. 

“We have no idea what a replacement unit costs; my husband (electronics tech by profession) decided to repair this 
simple circuit.  He cleaned up the dirty, overheated terminals, tightened (repeened) the rivet and soldered both terminals 
to the rivet.  Replacing the diode was also very simple, nothing special about that component he said, any small rectifier 
diode would work there.  Reinstalled the 'relay', everything works great.  Brake lights are brighter than before (wonder 
why?), and the IP warning lamp comes on when it should (either or both brake lights disabled and brakes applied). 

“For those interested, the XJ-S Parts Catalogue refers to this part as "Stop Lamp Failure Transmitter" P/N C.42291 
(actually this is a better name than 'brake warning relay', which is how the ROM puts it).  For anyone who knows which 
end of a soldering iron to grab, this would be a simple thing to repair.  Aside from the aforementioned diode, there is a 
transistor, a resistor, and two wire-wrapped reed switches inside the can.  All components could be easily replaced with 
like/similar items from any electronics store. 

“In case of on-the-road failures, we made up a simple "Y" jumper with male 1/4" spade terminals at the three ends to 
connect the three green/pink wires together.  This would bypass the transmitter and continue to allow the brake lights to 
work.” 

 

WARNING LIGHT TEST MODULE:  In several of the wiring diagrams, it is item #324, labelled an “invertor”.  In 
Fig. 13.99 in the Haynes manual, it is item #1 and it’s called a “Failure unit”.  In Fig. 22 in Section 86-22 of the 
Supplement to the ROM (same illustration as Fig. 13.99 in the Haynes) it is item #1 and called a “Warning light failure 
unit”.  Here’s what this thing does: when the starter is energized, this thing provides a ground circuit for the brake fluid 
level warning light, the handbrake warning light, and the oxygen sensor warning light.  As you’re operating the starter, 
these warning lights should glow.  This is to test the warning light bulbs themselves. 

 

 

Trip Computer

  

 

VARIATIONS:  The trip computer for US-spec cars has a different part number than trip computers used elsewhere.  
Since the Km/miles switch is readily apparent on all, Walter Petermann says, “It's probably due to the gallons.  Inside 
the trip computer there's a jumper labeled 'imp'.  All the trip computers (US) I've seen have this jumper missing.”