Jaguar XJ-S. Manual - part 142

 
 

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everything from A/C clutch control to EFI main relays.  Hella apparently came out with a replacement to “fix” the 
failures.  They haven’t been working.  Whenever I have a strange problem come in, 90% of the time it’s been one of 
these damn relays.  Unfortunately I’m forced to replace them with what Jaguar provides so that’s what they get.  The 
relays are developing bad contacts and overheat, failure is usually intermittent.  Most of these relays have a light blue 
case.  You can troubleshoot them by pulling the relay and jumping between the 30 and 87 terminals.” 

Leonard L. Peake adds, “There is a Jaguar "Service Bulletin" in regards to all relays on 1993 cars that have a date code 
before “183” stamped on the side.” 

Gary Penovich says uppity relays cause fault codes.  “To prevent it from happening again, you may want to replace the 
blue relay(s) with the updated black ones.  You should at least pull all your underhood relays, spray the sockets with 
electrical contact cleaner, and buff the grunge off of the relay contacts with an emery board.  I'll but they're covered in 
grunge and corrosion.” 

 

SHOPPING FOR RELAYS:  Finding a parts store employee here in the Bubba Belt who even knows what a relay is, 
much less whether or not it is the configuration you need, can be a challenge; “What kinda car is that fer?” as he 
prepares to type on his computer terminal.  Actually, the best place to look for relays is in a junkyard; just about all cars 
use relays for one thing or another.  They are often hidden inside fuseboxes or other compartments.  European cars 
often use Bosch relays.  All European automotive relays seem to have a little schematic on the outside, so it is a simple 
matter to confirm whether or not a relay has the desired terminals.  This author had no trouble finding relays that have 
the 87a (NC) terminal.  If you need a relay with only a single 87 terminal and don’t care what the fifth terminal is or 
even if there is one, almost any relay will work; they all seem to have the basic 87 terminal. 

If you find relays from late model cars, the schematic on the side is likely to show an internal diode or resistor wired 
around the coil (between the 85 and 86 terminals).  No problem; in fact, this is likely to be an improvement!  See the 
discussion on controlling inductive loads on page 557. 

 Japanese cars often use relays with a totally different configuration, and sometimes they have no schematic on the case. 
 They are very reliable relays, though, if you can figure out which terminal is which.  The layout of the base prevents 
plugging the wrong type relay into the socket, and the case color indicates which type relay it is.  Gee, some engineer 
there musta thought about what he was doing! 

If all else fails you can go to an electronics store and buy a generic “ice cube” 12VDC relay and solder short jumper 
wires to suitable spade connectors to plug into the original socket.  “Ice cube” relays are called that because they have 
clear plastic rectangular housings so you can see the innards; no schematic on the case required, you can see what the 
terminals are connected to!  Ice cube relays may have as many as four sets of contacts, and they always have both NC 
and NO contacts on each one.  If you buy a relay with more contacts than you need, just wire them all up to provide 
extra current capacity. 

 

 

Starting Circuit 

 

STARTER RELAY:  Also called the “ballast resistor starter relay” in the Haynes repair manual.  Item 194 on Jaguar 
wiring schematics.  It is Lucas style 22RA, Lucas part number 33356 or SRB301, Jaguar part number C36611. 

Most of the Jaguar schematics show this relay’s internals unclearly or even as a simple box with five terminals and no 
indication what goes on inside.  If you have a copy of Publication S 57, the “Electrical Guide”, the relay is shown in 
painstaking detail in Figures 2.1, 3.1, 4.1, 24.1, 24.2, 24.3 and 25.1 -- incorrectly every time.  The relay is shown as 
having only a single contact connected to terminals C1 and C4, while in fact there are two separate sets of contacts 
within the relay.  C1 and C4 are not connected to each other when the relay is not energized.  Also note that the C1 
contact is heavier duty than the C4 contact, so even though schematically it appears you could interchange them, it 
probably wouldn’t work long if you did. 

 
 

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If you’re having problems getting your starter to respond, perhaps the first thing you should do is attend to the spade 
connectors that attach to this relay.  See page 553. 

Dick Broxon of Cincinnati reports that his ’88 XJ-S would fail to start on damp mornings.  It wouldn’t even turn over, 
it would just click.  It would start later, though, when things had warmed up and dried out.  He removed the plastic 
cover from the relays under the hood on the right fender and sprayed them with a product called WIRE DRYER by 
Snap.  He has not had a problem since.  The starter relay, of course, is under the cover mentioned. 

Moisture is not the starter relay’s only problem.  It often turns out to be the culprit in a car that won’t start, or will fail to 
start sometimes and then work perfectly later.  To test, take the relay out of the car and apply power between the W1 
and W2 terminals; you can jumper from a car battery, or you can just poke a 9V battery down onto the terminals.  You 
should get a click.  Then connect an ohmmeter between C1 and C2, and check that the circuit closes when the relay is 
energised.  On this author’s relay, the resistance measured was random: less than 1 ohm one time, 25 ohms the next 
time, infinite ohms (open circuit) the time after that.  Click that relay a few times to make sure it makes good contact 
every time.  Note that clicking it a couple dozen times seems to clear it up so it makes good contact each time, but you 
probably shouldn’t rely on it staying good at that point.  If it doesn’t seem to be making good contact the first few 
times, it probably won’t make good contact the night you’re out on a date with the girl of your dreams. 

It may be that the contacts within the relay get a little charred.  It is possible to take the relay cover off, clean it up, and 
reassemble.  Unfortunately, this apparently doesn’t work for long.  Bill Farnsworth says, “I did that first.  A couple 
weeks later I found myself in a parking garage, as the best dressed mechanic in Redmond, WA. bent over the engine 
compartment wearing a tux...”  This author tried it too, with a remarkably similar experience to show for it. 

Just replace the stinkin’ relay.  Your local auto parts shop can probably order it for you, and it’ll cost you only about 
$60. 

Ouch.  OK, now we’re looking for reasonably-priced non-Lucas substitutes. 

 

STARTER RELAY SUBSTITUTE (OPUS):  Ask any auto parts shop for a starter relay for a Chrysler -- apparently 
just about any Chrysler from the late 70’s.  The particular starter relay this author found was made by Wells, number 
CR620.  This relay is electrically identical to the Lucas item; it’s just cheaper and better. 

The terminals are not labelled the same, of course -- and they are not arranged the same way on the base either, so you 
can't plug the wires on by location.  Here’s how to connect things up: 

 wire 

color Lucas 

terminal 

equivalent Chrysler terminal 

 BG 

W1 

I 

 WY 

W2 

G 

 WR 

C1 

EGR/SOL 

 N 

C2 

BATT 

 WU 

C4 

BAL 

The Chrysler relay is physically pretty similar to the Lucas, but the mount bracket attached to it is different.  You could 
just drill a new hole in your Jag and screw it down, but note that it’d probably last longer if it was mounted right side up 
with the terminals pointing down.  This author noted that the bracket on the Lucas relay was tack-welded to the casing. 
 I ripped it off, drilled some 1/8" holes in it and pop-riveted it to the bracket on the Chrysler relay.  Then I bent the 
Chrysler relay bracket down 90°, which put it in just about the same configuration as it had been on the Lucas relay. 

An alternative idea would be to open the new Chrysler relay (looks easy) and pop-rivet the Lucas bracket right to the 
case.  The Chrysler bracket, which is held on by rivets, can be removed and discarded and the holes covered.  
Reassemble and install. 

The Chrysler relay is also a bit larger than the Lucas -- which may entail some fiddling if you want to get that hokey 
plastic cover back over it.  I managed to get the cover back on; it wouldn't go on the OEM mounting holes, but it wasn't 

 
 

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too difficult to move it over a bit, drill two new holes and screw it down.  The upper edge is now not as close to the 
wing as it used to be, so you can see a bit of the bracketry by peering down in between.  But it looks OK. 

An alternative idea here would be to simply fab up a new cover with a hair more space than the OEM cover.  Just find a 
plastic box and start cutting sides off of it. 

One other minor difference of note: The Lucas relay appears to be a sealed box, but the Chrysler relay has a tiny filtered 
vent on the side of the cover.  Hmmmm. 

Lucas starter relay: special order, sixty bucks.  Chrysler starter relay: on the shelf, eight bucks.  You decide.  Wanna 
guess which one will be more reliable? 

John T. Richardson found yet another substitute relay:  “a Sorensen SR-17 relay, cost was $6 at Checker Auto Supply.  
While this is not an exact drop-in replacement, it does mount in the space available and anyone with a VOM can decide 
the correct wiring terminals.  Mine has been in service for over a year with no problems.” 

If you want to get down to basics, the starter relay is nothing more than a 12VDC DPST relay with one high-current set 
of contacts.  As with any DPST relay, you can substitute two SPST relays.  You can, in fact, wire up two standard 
automotive relays together to do this job, one to send power to the starter solenoid and one to send power to the ignition 
coil bypassing the ballast resistor.  A 30A rating on the one controlling the starter solenoid might be enough, or you 
might look for a relay with even higher contact ratings -- which will still be a sight cheaper than the Lucas starter relay. 

 

STARTER RELAY SUBSTITUTE (CEI AND MARELLI):  The Lucas CEI and Marelli ignition systems control the 
coil current electronically and therefore have no ballast resistor -- and therefore no need for a contact in the starter relay 
that bypasses a ballast resistor.  Nevertheless, Jaguar continued to use the same Lucas relay; in fact, parts lists seem to 
indicate they used it throughout the production life of the XJ-S.  So, you can still opt to replace it with the Chrysler 
relay described above for the OPUS cars.  There are some wiring changes from the pre-H.E. so here’s the connection 
chart for H.E. cars: 

 wire 

color Lucas 

terminal 

equivalent Chrysler terminal 

 WB 

W1 

I 

 WY, 

WU 

W2 

G 

 WR 

C1 

EGR/SOL 

 N 

C2 

BATT 

 WU 

C4 

BAL 

The C4 terminal doesn’t do anything on the Lucas relay, and the BAL terminal won’t do anything on the Chrysler 
relay. 

Not only is the C4 terminal still there, but the WU wire that went to the ballast resistor is still there as well -- at least on 
this author’s ‘83.  In fact, there are two WU wires; one is connected to the C4 terminal and goes nowhere; this is the 
one that used to go to the ballast resistor on the OPUS ignition system.  The other WU goes to the cold start timer, but it 
doesn’t connect to the C4 or BAL terminal; instead, it is connected to the W2 or G terminal along with the WY wire. 

The G terminal on the Chrysler relay only has one spade, so while you’re at the parts store you might want to pick up 
some of the doublers used to connect two female spade connectors to a single male spade terminal.  Or you can simply 
make up a short jumper with two male spade connectors and one female spade connector all tied together. 

So, you have a C4 contact that does nothing connected to a WU wire that goes nowhere.  That leads us to another 
possibility in starter relays: a relay that doesn’t have the ballast bypass contact at all.  Again, a Chrysler relay fits the 
bill; just ask for a later year, somewhere in the mid-80’s or so.  Chrysler likewise had gone to electronic coil current 
control and done away with ballast resistors, so they deleted that contact from their relays.  The terminals are the same 
as the chart above except there’s no BAL.  Just tuck that unused WU wire under something and forget about it. 

 
 

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Of course, once you’ve omitted the ballast bypass contact, you’re really just dealing with a plain ol’ SPST relay.  Any 
12VDC relay will work as long as the contacts are rated for enough amps.  It’s not known how many amps the starter 
solenoid pulls, but it’s entirely probable that a regular 30-amp automotive relay would work.  The W1 and W2 
connections become 85 and 86, C1 becomes 30/51, and C2 becomes 87. 

 

OTHER SWITCHES AND RELAYS INVOLVED IN STARTING:  If you are trying to use the EFI wiring diagram in 
the ©1982 Supplement, page 19-1, or Figures 13.10, 13.12, or 13.93 in the Haynes repair manual to diagnose starter 
problems, you may be getting very confused.  These diagrams indicate that the only thing that disables the starter relay 
is the “start inhibit switch” (on the shifter, also called a “neutral switch” or “automatic gearbox safety switch”, item 75 
on Jaguar schematics) via the “feedback monitor relay” (also called an “inhibit relay” or “feedback inhibit relay”, item 
355 on Jaguar schematics).  Why is a starter-disabling relay called a “feedback monitor relay”?  Judging from the 
diagrams it appears that the neutral switch on the shifter was originally intended to prevent starter operation in gear, but 
with the emission-controlled Digital P EFI it’s also needed to switch the EFI from open-loop to closed-loop operation -- 
and the neutral switch only has a single contact.  So, instead of adding another switch or providing one with more 
contacts, they installed this relay.  Since the relay likewise only has a single contact, it is used to control the starter, 
while the signal to switch the EFI -- being very low current -- is taken through the relay coil.  When the neutral switch 
is closed, the BG wire is grounded, the relay closes, and the EFI signal input sees 0V; when the neutral switch is open, 
the relay opens and the starter won’t work, while the EFI signal input sees 12V in the ungrounded BG wire. 

In the “UK & Europe” diagrams on page 19-2 of the ©1982 Supplement or Figures 13.9 and 13.11 in the Haynes, 
there’s no such thing as closed-loop operation and therefore no switching it on and off, so the feedback monitor relay is 
omitted and the starter relay is simply grounded through the neutral switch.  The starter wiring circuit on page 86-7 of 
the ©1982 Supplement shows this non-US layout with a simple connection from the starter relay through the neutral 
switch to ground. 

According to all of the diagrams mentioned above, the inertia switch will not affect the starter operation.  On the North 
American H.E.’s, though, the inertia switch does disable the starter.  There is an error in the diagrams showing the 
North American - Emission A schematic:  At the upper left in the schematic, there are six circles with numbers in them 
indicating where wires go to.  The leftmost one has the number 38, indicating either Ignition Switch Pin 1 (which 
would be a Start contact) or Ignition Switch Pin 3 (which would be an Ignition contact).  The fact that one number 
means both things indicates how screwed up things are here.  The leftmost circle should in fact be labelled 250, as it 
goes to the same place as the fourth circle from the left -- to the Inertia Switch.  On the Master Key, the second number 
38 should be scratched through, since the only remaining circle with a 38 in it goes to Ignition Switch Pin 1. 

It appears that, with the U.K. and Europe H.E.’s, the inertia switch will not disable the starter.  There wouldn’t have 
been a convenient way to do that without adding a feedback monitor relay, which otherwise wasn’t needed. 

The diagram for “Ignition, Alternator and Starter Systems” on page 86-7 of the ©1982 Supplement is likewise 
representative of U.K. and Europe cars but not North American cars.  For North American cars, the BG wire from 11 
(the starter relay) to 6 (the “Automatic gearbox safety switch”, what everywhere else is called a neutral switch or starter 
inhibit switch) actually should be a WB wire from the starter relay to the feedback monitor relay (not shown), and the 
feedback monitor relay is in turn controlled by the neutral switch -- and the inertia switch (not shown). 

There are other changes you can make to that diagram while you’re there.  On item 11 the upper right terminal is W2 
and the lower right terminal is W1, and these are the coil terminals.  The upper left terminal is C1 and the lower left is 
C2, and these are contact terminals -- and C4 is omitted from this diagram, which is just as well because it doesn’t do 
anything.  On item 7, the two terminals on the left are the coil and the two terminals on the right are the contacts.  On 
item 4, the six terminals, clockwise starting with top center, are 4-3-2-6-1-5.  On item 12, the wire connecting to the 
bottom terminal is WS/U, not WS. 

The wiring is shown correctly for North American cars in Figures 2.1, 24.1, 24.2, and 24.3 of Publication S 57, 
“Electrical Guide”.