Jaguar XJ-S. Manual - part 143

 
 

567

STARTER SYSTEM TROUBLESHOOTING:  MacDonald suggests the ultimate test to determine whether your 
starting problems are caused by something in the relays and wiring or by the starter itself:  “Try bypassing the thick 
brown with the thick white/red wire at the starter relay.  If the starter does not crank then it's your starter!”  Or the heavy 
cable wiring from the battery to the starter. 

If the starter itself is working and therefore you must have a problem in the wiring to it, the next thing to try is to 
disconnect the WB wire from the W1 terminal on the starter relay, and connect a ground wire to the W1 terminal 
instead.  If the starter now works like it should, your starter relay is OK (or intermittent!) as well as the wiring from the 
ignition switch; you now need to be looking at the inhibit relay (under the same cover as the starter relay), the neutral 
switch on the shifter, and the inertia switch. 

 

 

Starter

 

 

Jaguar provided a new design starter beginning in 1988 that features a gear reduction drive.  This starter will fit earlier 
V12’s, and is much smaller, much lighter, more reliable, and just all-around better.  If you ever need to replace the 
starter, insist on the gear reduction model. 

 

STARTER REMOVAL:  Both the ROM and the Haynes manual list several steps involving the steering column.  This 
must reflect RHD cars; you don’t have to mess with the steering column at all in a LHD car. 

David Johnson wants everyone to be aware that the upper bolt holding the starter in has a 12-point head, and therefore 
requires a 7/16” 12-point socket.  The manuals simply say to remove the bolts.  “You can't really see the bolt head even 
with a mirror.  So because most bolt heads are 6 point, I tried for what seemed like days with several different size 
sockets.”  Note: Davide Frada says an 11mm 12-point socket worked on his 1980; 11mm is just a hair smaller than 
7/16”.  There are some who claim it’s a 1/2” 12-point head on early models.  Whatever, it’s a 12-point head; keep 
trying until you find the size that fits!  Some have suggested replacing this bolt, either with a longer bolt with a regular 
head and a sleeve under it or with an Allen head cap screw, but really once you know it’s a 12-point head it works OK 
as it is. 

“Also I learned not to remove the transmission dip stick and tube.  What a mess!  I guess with the car up on ramps the 
fluid ends up being significantly higher than the bottom of the tube.” 

Doug Maury wrote up a lengthy play-by-play on removing the starter.  I won’t include it all here because it’d add 
several pages to this book, but I will include some key points: 

The front end of the car should be placed on jack stands so that the crossmember is at least 18” above the ground.  And 
don’t forget to disconnect the battery. 

The RH air cleaner, RF wheel, and RH downpipe all get removed.  Turn the steering wheel all the way to the left. 

Remove the starter heat shield and cable retaining clips.  Disconnect the big cables from the solenoid, including the one 
from the alternator.  An 8” extension and a deep socket are suggested here. 

Maury suggests disconnecting the “ignition” wire (red and white -- the only small one to the solenoid) at the other end, 
up in the vicinity of the transmission dipstick, and leave it hanging from the starter as it comes out.  Remember to put a 
wire onto the new starter before installation. 

There are two bolts holding the starter in place: one that’s obvious and easy to get to, and the hard-to-get-at one with 
the 12-point head described above.  It’s a good idea to leave the obvious one in place to hold the starter until you get the 
difficult one out.  Disconnect the vacuum line to the modulator on the transmission.  If you left the center section of the 
exhaust pipe in place and held it up with a piece of wire, you might want to unhang it at this point so you can move it 
around.  Use of a couple of ratchet extensions and a swivel is recommended on that difficult bolt.  Some prefer to keep 

 
 

568

the ratchet handle forward of the transmission mount while others prefer to use really long extensions and feed them 
through above the transmission mount to get a straighter angle on the bolt. 

Once loose, the starter can be a tight squeeze to get out, but it’ll come out with some twisting and finagling. 

Maury suggests replacing all the cables and wires, since they’ll have been well baked by the proximity of the exhaust 
system.  Good advice, although obviously the new cables will soon be baked as well.  Going with something with high-
temp insulation would be good, but in the case of those huge cables the more likely tactic will be simply making sure 
they’re not bumping anything that they could short out against. 

Upgrading the cable to the alternator while you’re in there is highly recommended, just in case you ever replace the 
Lucas alt with something that puts out serious amperage.  See page 579.  When Alex Dorne replaced the early heavy 
starter with the later geared starter, the original alternator cable was too short to reach the smaller starter -- another 
reason to replace that wire! 

Dorne also fabbed a bracket to hold the original heat shield over that new smaller starter.  “The bracket is installed on 
the end of the starter, held by the two nuts that hold the starter together.” 

Maury suggests you check the new starter before installing it, including checking the solenoid travel (see below).  If 
there’s anything outta whack with that rebuilt starter, you’re gonna kick yourself for not checking it before installing. 

 

SOLENOID TRAVEL ADJUSTMENT:  Apply 12V to the solenoid connection and watch the pinion move.  Check 
that the solenoid moves the pinion to the specified position so that a .005” feeler gauge will fit between the pinion and 
the thrust washer but a .015” feeler gauge will not.  If it’s out of spec, it can be adjusted by repositioning the eccentric 
pivot. 

Roger Bywater:  “If wrongly adjusted the solenoid can reach end of travel without the power contacts being properly 
made to complete the circuit to the motor.  Because the power contacts can burn if not solidly home it is possible to get 
a marginal condition where the effects of expansion can allow it all to work normally when cold but not when hot.  I 
suspect that a lot of starter motors have been condemned as failed when proper adjustment would have made them 
serviceable. 

“Unfortunately the pivot adjustment faces the engine block so cannot be altered in situe.  It is therefore a good idea to 
check the end clearance adjustment on any starter whenever removed or when fitting even a new one.” 

Hmmmm.  Sounds like it might be a good idea to aim for the .015” end of that range. 

 

SOLENOID TERMINALS:  Walter Acker IV says, “There is one major design problem in the GM starter/ solenoid 
system.  The problem is that the top stud that holds the main cable that goes into the solenoid is too short in that the unit 
does not have enough length to accommodate a split ring lock washer to keep it tight and reduce the amount of arcing 
that happens in this unit.  The answer is to go to a local hardware store and purchase a small package of 3/8” “inside 
star” lock washers and use one between the nut and the Bakelite housing that is on the solenoid. 

“I just checked my ROM and the starter system for the XJ-S uses this type of system also, but the size of the lock 
washer may be a slightly different size.” 

 

INTERMITTENT STARTING WHEN HOT:  The symptom: the car will start every time when cold, but when hot 
sometimes the starter doesn’t even budge.  Phil Boylan says, “In my opinion you may be suffering from the infamous 
"starter heat-soak" problem that is common to vehicles with a GM-style starter solenoid mounted with the starter motor 
in the high-heat area near the exhaust manifolds.  The heat weakens the solenoid electrically such that the relay does not 
actuate reliably when starting current from the ignition key switch is applied. 

“I went through two Lucas starters (one rebuilt, another brand new -- $$$), replaced the transmission micro-switches, 
upgraded the battery and ground cables, plus a bunch of other desperation fixes that shouldn't have worked (and didn't). 

 
 

569

“Finally, I bought a "GM hot start kit" for $29 that electrically bypasses the starter solenoid switch and adds a Ford 
style remote starter solenoid.  I mounted the remote solenoid in a convenient location on the passenger side firewall.  
The factory solenoid stays put because it's required to actuate the starter bendix gear.  All you're doing with the remote 
solenoid is re-routing the ignition and battery cables first to the remote solenoid and then on to the factory 
starter/solenoid terminals such that the high amperage relay switching occurs in the cooler location. 

“That small, inexpensive mod completely solved my hot start problems and the symptoms have never returned.  The 
remote solenoid also provides convenient access to the ignition circuitry instead of having to feel blindly under the 
engine manifolds. 

“And since Ford now owns Jaguar it can be argued that the remote solenoid backfit is also correct in spirit. :^)   ” 

 

STARTER SLOW TURNING:  Mike Morrin:  “Check that the engine grounding cable (underneath on the left hand 
side) is not loose or damaged.  This is not particularly an XJ-S fault, but it was loose on mine, and I would have been 
really mad if I had pulled the starter before discovering it.” 

The fact is that lots of electrical gremlins have been traced to faulty grounds, a lot of them to this strap in particular -- 
see pages 267, 323 and 553. 

Of course, when a starter is turning slowly, most mechanics will check the battery terminals for corrosion.  On most 
cars, one cable goes straight from the battery to the starter solenoid and the ground cable usually connects nearby, so a 
bad connection would almost have to be at the battery.  On the XJ-S, however, the power to the starter comes from the 
battery along the bottom of the car and up to the left side terminal post on the firewall, then over to the right side 
terminal post on the firewall, then down to the starter solenoid.  Weak connections can therefore be at either terminal 
post on the firewall as well as at the battery.  See page 556 for more on those terminal posts. 

 

 

Alternator

 

 

If there is any indication that your alternator is having trouble (not charging, low voltage, etc.), you should have it 
attended to immediately.  If caught soon enough, it can be repaired or rebuilt.  If left alone, it self-destructs and a new 
one is required. 

One indication your alternator has had it is that the alternator warning light stays on after the engine is shut off. 

An automotive alternator can be more thoroughly checked using a VOM (preferably digital).  Connect the VOM 
anywhere that will show system voltage -- the cigarette lighter is convenient.  If the engine is turning fast enough for 
the alternator to produce adequate power, usually about 1500 rpm, the system voltage must be between 13.6 and 14.4 
volts.  If it is not, either the alternator is defective, or there’s a problem with the connections to the alternator, or there is 
a huge load somewhere draining all the power, or there is a problem with the belt drive turning the alternator. 

Even if the voltage is between 13.6 and 14.4 volts, there still may be a problem with the alternator, because it contains 
diodes that rectify 3-phase alternating current into the direct current the car uses.  If one diode fails, it will still put out 
13.6-14.4V, but far fewer amps.  And the output gains a lot of “ripple”, meaning it looks less like smooth direct current, 
it’s got some large fluctuations in it. 

 

ALTERNATOR EXCITATION:  The field on the XJ-S alternator is excited through the “ignition” warning light (fifth 
from left on the author’s ’83, has a little picture of a battery), so if this light is burnt out or disconnected charging may 
be intermittent.  According to Randy Wilson, “A common enough design.  Lots of alternators will respond like this... 
some would never charge.  Here’s what happens:  the alternator needs a signal to indicate the key is on, and a power 
source to boost itself into a charging condition... bootstrapping, if you will.  This power requirement is low enough that 

 
 

570

a lot of alternators use the power flow through the charge light for this purpose.  This is called the exciter.  And, in 
reality, key on is not really an important condition to the alternator.  You just don’t want to be driving the exciter full 
time, lest your battery will go flat overnight.  Once the alternator is charging, it becomes self-exciting, and no longer 
needs or uses this external power source (oversimplification).  Thus the light goes out. 

“The exciter is used to induce enough of an electromagnetic field to start the current generation.  However, there is 
always some residual magnetism floating around in a used alternator.  With this residual, the alternator can generate a 
little bit of current, if you spin them fast enough.  In the case of Lucas (and others) the current needed to self-excite is 
fairly low -- low enough that the current from the residual magnetism can meet the demand.  This usually happens at 
2500-3000 engine rpm.  And as soon as the alternator is up and charging, operation is as normal.  You don’t have an 
outside exciter source, but you don’t need it any more.” 

Jaguar may have provided a fail-safe here.  The electrical diagrams show a 100Ω resistor in parallel with the alternator 
warning light, which would seem to mean it would get some excitation current even when the bulb is burnt out. 

 

ALTERNATOR TROUBLESHOOTING:  Michael Minglin says, “I really like the factory manual’s instructions for 
checking maximum amps output.  Even If I could reach down there to remove the plastic cover, I could not see to 
connect a jumper between “F’ and “-”.  My solution was to remove the alternator and attach wires from “F” and “-” and 
run them out of the back of the alternator, up the inside of the fenderwell, with a male and female connector on the end 
by the cross brace.  Now to jump the regulator all I have to do is connect the connectors.  I’m not sure it is worth 
pulling the alternator just to make these connections, but I will never put in another alternator without this 
modification.” 

If your alternator doesn’t seem to be charging like it should and you can’t find an electrical cause, don’t overlook the 
mechanical problem described on page 90 -- especially if it’s a later car with a Bosch alternator and a ribbed alternator 
belt, and especially if it’s a convertible. 

 

RELOCATING DIODES:  An alternator contains a full-wave rectifier, which is an assembly of six diodes that convert 
the alternating current produced by the windings into direct current for powering the electrical loads in an automobile.  
Conveniently, these devices are built right into the alternator, so service is simple: just remove the bad alternator and 
install a good one. 

Unfortunately, the heat inside the Jaguar engine compartment is not good for electronic semiconductor devices such as 
diodes.  The alternator has a cooling fan and the diodes are built into a heatsink, but when it’s hot everywhere in the 
engine compartment such efforts will do no good. 

If you’re sick and tired of replacing diodes (or alternators), one possible solution is to open the alternator up, take the 
diode assembly out, and relocate it to some remote location where things are cooler.  You will need to provide a small 
fan to keep them cool (they generate a good deal of heat on their own!), but a 12V computer fan is cheap and workable. 
 Craig Sawyers sizes the wires needed: “the current from each of the three phases to the diode pack will be around 1/3 
of the total output current.  In the US, this would be known as 12 AWG, in Europe 3mm

2

.  The output cables to the 

battery post would have to be rated at the full 120A.  A double run of 8 AWG (8.4mm

2

) would do this nicely (it will 

handle 150A).” 

Another nice feature of this mod is that you no longer need to use expensive Lucas diodes; you can buy a diode pack 
used to rebuild any generic alternator of comparable or greater amperage -- the GM ones are really cheap in the US.  
You could also opt to improve the alternator by using Schottky diodes, which have a lower threshold voltage and 
therefore rob the alternator of less of its power and generate less heat. 

And don’t forget: if you locate the diode pack somewhere convenient, it should be a lot easier to work on than the 
alternator, which is a real pain to get to.