Jaguar XJ-S. Manual - part 161

 
 

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Figure 36 - Headlight and Fog Light Wiring 

 
 

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The headlight switch in the US-spec 1983 H.E. has five positions, three above and one below the off position.  To get 
into the top or bottom position requires pushing the knob in while turning.  The connections made in the positions are 
as follows: 

 

 

 3:  1-2-3-5 

 

 

 2:  1-2-3-4 

 

 

 1:  1-2-3 

 

 

 0:  No connection 

  -1: 

 

1-2 

The -1 position, connecting only the dash lights and right side parking lights, apparently serves no intended purpose; as 
wired, all the parking lights come on due to backfeed through the bulb failure sensors.  After a few seconds for the bulb 
failure sensors to warm up, the left side parking lights dim.  If an owner wished, however, it would be a simple matter 
to rewire the right side parking lights to terminal 3 and use the -1 position to operate the dash lights only. 

Other headlight switches are different, however.  John Himes says that on his US-spec ’88 the positions are: 

Off 

Parking lights only 

Headlights 

Headlights & fogs 

Fogs only 

John Goodman reports “On UK cars the fog/driving lights are operated on the rotary dash light switch. 

1= side/park 

2= headlights 

3=  head & fog/driving lights 

4=  side/park & only fog/driving lights 

...and there is a push facility that works when in position 2-4 for the rear fog warning lights fitted in the rear bumpers.” 

 

HEADLIGHT SWITCH KNOB REMOVAL:  To remove the headlight switch knob, you must depress a button in the 
shaft that is behind the surface of the dashboard and points down.  To reinstall, you merely need to push the knob on, 
because it is shaped to slide over the shaft button and snap in place. 

 

HIGH/LOW BEAM RELAY:  Also known as the main/dip relay.  In some manuals, the schematics of the high/low 
beam relay (Jaguar part no. C38616) show the components between connections 56, 56a, and 56b to be a normal set of 
relay contacts.  This is not actually the case.  This device is an electrically-operated rocker switch; when the coil is 
energized, the contact is switched from one side to the other, and remains there when the coil is de-energized.  Next 
time it’s energized, it flips back.  Jaguar wants some serious $$$ for that relay. 

Roger Homer reports that other cars use a similar relay.  “The Headlight Relay is the same as the one on an early model 
Torana (General Motors Aust).  They used the same high/low switching system, the relay I found is made by SWF 
(Germany?) part no stamped on relay is R200.867.” 

 
 

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Ray Reynolds provides another report:  “I found a compatible unit that dropped right in.  I had to drill an extra 
mounting hole in the fenderwell to bolt the 
new relay in, but all the connectors plugged 
right in, and it all fit under the stock relay 
housing (with a little bending around of the 
headlight wires).  The relay itself looks like 
a Potter & Brumfield, and was part 
#PBS89R from Micro Alarm (in Vernon, 
CA).  It has 2 microswitches on top that do 
the actual power switching.”  Reynolds 
notes that this relay does not provide the 
pull-to-flash feature the stock relay does, 
but it would be easy enough to add a normal 
relay with the coils wired in parallel to 
provide this function.  “Since the plunger is 
visible, you might be able to bolt another 
microswitch to the bottom of the relay so 
that it is activated when the relay is tripped 
for the flash feature.” 

If your high/low relay has given up the 
ghost and you can’t find a reasonably-
priced replacement, an alternate scheme 
using three conventional relays and a diode 
is shown in Figure 37.  Note that wiring 
(and related contacts) indicated by heavy 
(red) lines must be suitable for headlight 
current, 30 amps or so.  All other circuits 
are less than 3 amp.  For the diode, a Radio 
Shack cat. no. 276-1661 will do nicely.  Of 
course, you will need to figure out where to 
mount these relays; perhaps in the space 
behind the left headlights. 

As with any such circuit, a single multi-
contact relay may be replaced by multiple 
single-contact relays by simply wiring the 
coils together.  This may make sense here, 
allowing the use of SPDT 30-amp relays 
along with tiny “ice cube” DPDT relays instead of trying to locate DPDT or 3PDT 30-amp relays. 

The only functional difference with this circuit from the original is that your headlights will always be on low beam 
when you first turn them on. 

 

HEADLIGHT BUZZER:  The XJ-S doesn’t have one!  What a cheap car.  To add one is easy.  You need a 12 volt 
buzzer such as catalog no. 273-055 from Radio Shack, and a rectifier (or diode) such as catalog no. 276-1661.  For the 
buzzer you can also use any buzzer you’ve ripped out of a car, such as those pesky seat belt buzzers. 

Connect one of the headlight wires to one end of the rectifier.  Connect the other end of the rectifier to one lead of the 
buzzer.  Connect the other lead of the buzzer to one of the ignition wires.  Both of these wires are near each other under 
the dashboard -- from the headlight switch and the ignition switch. 

A rectifier allows current to flow in only one direction.  If you have wired it correctly, when both the ignition and the 
headlights are on, there is no current flow because both wires are at 12 volts.  When the ignition alone is on, there is no 

81a

56a

56b

56

31b

 

Figure 37 - High/Low Relay Replacement Scheme 

 
 

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flow because the rectifier stops it from flowing that way.  When the headlights are on but the ignition is off, current 
flows and the buzzer buzzes.  If the buzzer buzzes when the ignition is on and the headlights are off, reverse the 
rectifier. 

Jan Wikström did it a different way:  “Pulling the key out also operates the switch that controls seat belt warning etc.  
As my car doesn’t have those, I’ve used it to operate a “headlights on” warning buzzer.” 

Connie Vloutely says, “I have been wanting to do this for a long time but could not find chime element suitable for 
automotive use.  One that works on 12 Volt DC.  I hate buzzers.  I found one in the local radio shack store P/N  RS-
273-071.” 

 

HEADLIGHT UPGRADES:  When you’re driving your Jag down some desolate two-lane blacktop road at 140 mph 
on a moonless night, it’s helpful to be able to see where you’re going.  Unfortunately, not all headlight systems are up 
to the task.  If you have the US-spec four round headlights with the original sealed beam units in place, I suggest you 
slow down.  

Even if you obey all posted speed limits, you will be amazed at what an adequate set of headlights will do for the 
pleasure and enjoyment of nighttime motoring.  Where you used to have to squint and stare in hopes of seeing things in 
time to avoid hitting them, you can now sit back and relax.  In fact, you may come to fully appreciate the advantages of 
nighttime driving, with the reduced traffic and cooler temperatures. 

 

RELAY INSTALLATION:  If you wish to improve the headlights on your car, the first thing you should do is install a 
set of control relays.  This will improve the light output of the stock headlights, whatever type they are, and may just 
satisfy your need for better light -- and is a perfectly legal modification.  If you decide to replace your headlights with 
something with higher wattage (as suggested on pages 650, 652, and 653) you will not be happy with the results unless 
you install control relays; the additional losses in the stock wiring due to the increased current flow will rob you of any 
increase in light output. 

The whole idea of installing relays is to get as much of the battery/alternator voltage to the headlights as possible, since 
a small reduction in voltage makes a big reduction in light output on incandescent lights.  Low voltage also causes 
incandescent lights to appear yellowish, which diminishes visibility even more. 

Your objective, therefore, is to provide wiring that gets the power from the battery/alternator to the headlights with big 
fat wires and as directly as possible.  Unfortunately, that wasn’t the objective of the guy who designed the wiring for 
your car; his objective was to provide wiring as simply and cheaply as possible, and sized just big enough to keep it 
from melting.  So, the stock wiring goes from the bus on the firewall down to under the dash, through the headlight 
switch, back to the front left corner of the car, through the main/dip relay and the headlight fusebox, then out to the four 
headlights -- all with wires that are barely adequate for the sorry headlights that came with the car. 

A simple confirmation of the problem is to remove the headlights from their mounts while leaving them connected, 
start the engine, turn on the headlights and measure the voltage right at the connections on the back of the bulbs.  The 
voltage there should be within a half a volt or so of the voltage measured between the terminal on the firewall and the 
chassis under the same conditions (headlights on, engine idling).  If the voltage is much lower, the installation of relays 
will help the light output considerably.  If you’d like to confirm where the losses actually occur, measure between 
different points along the line, starting with the terminal on the firewall and including both ends of each fuse in the 
headlight fusebox as well as the terminals on the headlights.  If you measure the voltage between the terminal on the 
firewall and the power connector on the headlight, you will be measuring the total loss of the wiring system except for 
the ground circuits.  You can also measure parts of this loss, such as between the fuse and the headlight, between the 
firewall terminal and the fuse, even across the fuse itself.  If you measure the voltage between the ground connector on 
the headlight and the chassis of the car, you will be measuring the losses in the ground wiring (which are significant -- 
the ground wiring is inadequate, too). 

If your voltage losses are too high, the solution is to disconnect the wires from the headlights and connect them to the 
coils of relays, run a massive power wire from the terminal on the firewall to the common contacts on the relays, and