Jaguar XJ-S. Service manual — part 138

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TEMPERATURE SENSORS: Martin Sellars says, “Temperature Sensors: the Delanaire system uses three, all are
electrically identical. They measure ambient air temperature (mounted on the RH blower housing), in car temperature
(above the glove box, behind a small aperture in the dash) and on the evaporator. These have three wires to them,
power (5Volts from the ACC), ground, and the output wire. The output voltage is very closely controlled at 2.785V at
0°C and rising by 0.01V per degree C. So, a sensor at 20°C (about 68°F) should read 2.985V, and at 30°C (about
90°F) should read 3.085V, and so on. I found these can be measured reasonably easily with a standard 20k/Volt
moving needle “hobby” type multimeter, at least well enought for fault finding purposes.”

Richard Mansell quotes from a Jaguar publication on the changes for the 1992 model year:

“The air-conditioning in car sensor now uses the motorised aspirator/sensor from the XJ6 allowing a more accurate
reading of the true temperature of the cabin which will be less susceptible to drift or overshoot.”

DUMB PROBLEMS: Martin Sellars: “My car showed very erratic operation of the A/C, sometimes OK, sometimes
wrong settings (hot on hot days and vice versa!), sometimes no action at all. This fault might have been blamed on the
computer - but in fact it was due to moisture coming out of the evaporator, and running down the RHS of the
transmission tunnel onto the inline fuse holder that carries the supply current to the A/C computer. The contacts had
corroded slightly, breaking the supply current, and giving intermittent operation of the A/C. A new inline fuse, plus
fixing the drainage, solved the problem.”

WHILE YOU HAVE THE BLOWERS OUT: Martin Sellars: “While the blowers are out, access to the evaporator is
much easier. The four short tubes which couple the evaporator body to the rubber blower ducts can be twisted slightly
and removed. This allows slight access to extract some of the gunge and detritus that blocks up the drainage system,
causing wet carpets, rusty floors, and other problems.”

HEATER CORE REPLACEMENT: Those who must replace the heater core should thank their lucky stars if they
have the Delanair MkIII system. A major design feature of this system is the ease of replacing this core, a major task
on the earlier cars. The Delanair MkIII system has bolt-on pipes for the heater core, eliminating the need for the
“shortcut” pipe-cutting procedure devised for the earlier system. Also, Per Michael Neal, “The heater core is
removable from the right side. There is a large piece of black tape, similar to electrical tape, that covers the access
panel. Removal of the core is simple as unbolting the pipes, pulling the glovebox and access cover and removing the
core.” This eliminates the need for removing the instrument panel and dropping the steering column, as on earlier
models.

HEATER CORE PIPE ATTACHMENT BOLTS: Per Julian Mullaney, “There was a problem of dissimilar metals
causing corrosion of the bolts which attach the pipes to the brass core. The pipes and heater core are brass, the screws
holding them together were steel. I guess stainless bolts would be better. You could replace them as a preventive
measure.”

HEATER CORE PIPE ATTACHMENT O-RING SEALS: Per Julian Mullaney, “The O-ring seal used at the
connection point appears to be of a terrible design. A mechanic once told me that these O-rings always go first.”

For anyone who doesn’t think the resultant leaks would be a big deal, Mullaney adds: “This leak really screwed up a
lot of stuff under there. The drips ruined the A/C amp, connectors, and my CD player.”

Apparently Jaguar realized the seriousness of this problem. According to Michael Neal, “Jaguar has a gasket to replace
the O-rings. It is shaped like the mating pipe of the heater core and is made out of a silicon/rubber type material.” The
part number for the gasket is JLM 759; you need two to do the job.

According to Mark Roberts, the “condensation deflector shield” being added to systems by Jaguar (see page 662) is
actually a result of these connections leaking on radios!

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HEATER CORE: Peter Cohen found this note: “When stock of this heater core is depleted use part number JLM
11343. The pipes that are bolted to the JLM 11342 must be removed and re-attached to the JLM 11343 because they
have a different angle than the pipes on the JLM 11343. This mild modification is necessary because of the price
differential between the JLM 11342 & JLM 11343.”

Steve Gibson explains: “Both parts are still listed by Jaguar at the present time. The JLM11342 Heater Matrix was
fitted to the XJ12 Series III 1985 onwards as well as the XJ-S 1987 onwards. The JLM11343 Heater Matrix was fitted
to the XJ40 1987 to 1993. The JLM11342 is just short of being twice as expensive as the JLM11343 unit, so I should
forget about "when stock is depleted" and if you have need of a replacement get the later unit and save yourself some
money.”

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ELECTRICAL

COLOR CODING: In electrical diagrams, this book uses the same wire color coding scheme as Jaguar uses in their
manuals. If two colors are indicated, the first is the base and the second is the stripe. If three are indicated, the third is a
spiral stripe. The color codes are as follows:

N - browN (not neutral!) - usually 12V power

B - Black - usually ground

U - blUe

K - pinK

S - Slate (British for gray)

G - Green

Y - Yellow

O - Orange

R - Red

W - White

P - Purple

Jaguar also throws an L in occasionally to indicate a Light color.

If you want to know more about wire color codes, perhaps you should consult BS-AU7a, “1983 Colour Code for
Vehicle Wiring”, British Standards Institution, 2 Park St., London W1A 2BS. Tom Bennett points out that an extract
from this code is available on the WWW at:

http://www.dimebank.com/tech/LucasColours.html

This site also says you can get suitably color coded wire for harness repairs from British Wiring (page 703), British
Pacific (page 703), and Narragansett Reproductions (page 705).

WIRING DIAGRAMS: If you’re going blind staring at the diagrams in the ROM, Michael Frank sends this tip:
“Wiring diagrams in the following sizes (prices in British Pounds):

500mmx353mm

£9.95

+ £1.50 postage

594mmx420mm

£12.95

+ £2.00 postage

840mmx594mm

£19.95

+ £3.00 postage

1180mmx840mm

£34.95

+ £4.00 postage

Available for most classic Jags, with XJ and XJ-S available soon. The diagrams are laminated in plastic and color
coded to match the actual wiring. The supplier is:

Classic

Graphics

11 Springhill Grove

Stockton, Cleveland TS17 OYW

England

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ELECTRICAL GUIDES: Jaguar offers booklets full of schematics for the electrical systems; these don’t seem to have
a title, but they are generally called “Electrical Guides”. Of course, you want to know which one to get, but that’s a
little complicated. Allow me to explain: One of these booklets says “Publication S 57”, “Revised 7/88”, and has a
leaper on the cover. Inside, it has three sections: Series III XJ6, XJ-S through 1987 MY, and XJ-S 1988 MY. Each has
its own table of contents. Hence, when you buy a copy of “Publication S 57” and tell the seller what kind of car you’re
buying it for, you probably won’t get the entire booklet; you’ll only get the section you need. Since the cover doesn’t
mention the models covered, you get a copy of the cover and one of the three sections and the impression that you have
gotten the entire book. This isn’t really a problem except that owners of pre-87 H.E.’s, ’88 H.E.’s and Series III XJ6’s
all own “Publication S 57” and wonder what the other guy is doing with it.

Also: that one section may claim it covers “XJ-S through 1987 MY”, but it lies. It only covers H.E.’s, so it really
covers only 1982-88. If you have a pre-H.E., you may be out of luck here; presently there is no comparable help for the
pre-H.E. There is enough difference between the pre-H.E. and the H.E. that trying to use Publication S 57 on a pre-
H.E. will cause more confusion than it clears up.

Richard Mansell provides a comprehensive list of Electrical Guides for the XJ-S:

S 57

XJ6 Series III, 1987 & 1988 XJS Electrical Guide

S 57/89

1989 MY XJS Electrical Guide

S 57/90

1990-91 MY XJS Electrical Guide

S 72/92

1992 MY XJS Electrical Guide

S 72/93

1993 MY XJS Electrical Guide

S 72/94 4.0L

1994 XJS 4.0L Electrical Guide

S 72/94 V12

1994 XJS 6.0L Electrical Guide

S 72/95 4.0L

1995 XJS 4.0L Electrical Guide (thru VIN 198334)

S 72/95 V12

1995 XJS 6.0L Electrical Guide (thru VIN 198334)

S 72/96 4.0L

1995/96 XJS 4.0L Electrical Guide (VIN 198335-on)

S 72/96 V12

1995/96 XJS 6.0L Electrical Guide (VIN 198335-on)

This author has the 82-87 section of S 57; it is a loose-leaf binder containing 25 pairs of figures. In each pair, the first
figure is a schematic of a particular electrical subsystem, and the second figure (on the facing page) is a plan view
drawing of the engine or car indicating where the individual components are located. Some of the illustrations are 8½”
x 11” and some are larger fold-out pages. This is very useful information, but note that the publication does not include
any text at all; no descriptions of how systems work, no troubleshooting info, nothing. Since the supplements to the
ROM do include such descriptions and troubleshooting info, they are perhaps the more useful guides even though the
schematics are not as clear and complete.

Peter Cohen adds, “...the S57/year wiring diagrams are put out by Jaguar Cars of North America, and would not cover
RHD or be available in the UK. OTOH, they are just books, easy to ship (and light), and should be duty free. I'm sure
Jag Services would post one anywhere if you paid by credit card.”

Regarding the electrical guide for his ‘90, Mike Wilson says, “They now come with a Supplement that includes
corrections for the following:

Fig 2.1: Added Diode to Neutral Switch circuit

Fig 2.2: Added Diode to Component location

Fig 6.2: Added Shorting Plug behind Fog Light Relay

Fig 11.1 & 12.1: Corrected the Titles for Coupe and Convertible

Fig 15.1: Ground Code Correction for heated rear window