Jaguar XJ-S. Manual - part 162

 
 

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run substantial wires (with suitable fuses) from the contacts on the relays to the headlights.  Thus you operate only these 
new relays with the original wiring, switch, and main/dip relay, and the serious current for the headlights themselves 
takes a much more direct route from the battery/alternator through the contacts in the new relays straight to the bulbs.  

This mod only requires the locating of relays and running a serious cable from the terminal on the firewall to whereever 
the relays are; this author used a 4 gauge, but a 6 gauge cable would actually be enough.  The relays should be mounted 
somewhere near the headlights to minimize wire length; perhaps within the boxes directly behind the headlights 
themselves.  John Napoli suggests a big fuse in that cable, since the relays are likely to be located out at the front corner 
of the car and may be shorted by a relatively minor collision, and the shorting of such a major cable may cause serious 
problems. 

Technically, you can do this whole job with only two relays, one for low beam and one for high beam, but it may be 
preferable to use two for high beam to keep from overloading the contacts on a standard 30-amp relay.  Note that 
simply wiring two relays in parallel may not have the desired effect of doubling the contact capacity, since one will 
always close a millisecond before the other and thereby take all of the arcing load.  A much better idea is to separate the 
wiring to the high beams and have each relay handle half the headlights.  That way, each relay will only see half as 
much load, and if one circuit fails it only kills half your high beams rather than all of them. 

Of course, you’ll probably want to install a relay for the fog/driving lights as well. 

Having four individual fuses on circuits that operate nothing but relays is definitely overkill.  On the XJ-S, it makes 
more sense to continue to use the existing headlamp fusebox to serve the headlights themselves, so the relays should be 
wired into the circuits before the fuses.  On the ‘83, the headlamp fusebox can be fiddled with by drilling out the two 
rivets that attach the mounting bracket to the fenderwell.  The bracket isn’t welded to the flange on the edge of the 
engine compartment, just folded over it.  Removing the rivets allows the bracket to be lifted away, which in turn allows 
the fusebox itself to be turned over and the wiring rearranged.  You can reinstall the bracket with a couple of screws, 
making it easy to work on in the future.  Later cars have all sorts of variations in the fusebox in this area, but any of 
them can be altered as necessary. 

Tip for those with the 4-headlight system:  The existing wiring from the fusebox to the high beams on each side of the 
car is inadequate for both high beams, but it’s good enough for one.  So, one possibility is to run a new wire (about 12 
gauge) to each side of the car with a new inline fuse for one of these high beams and reuse the existing wiring and fuse 
holder for the other high beam.  The small wire from the 3-prong connector right behind the headlights to the headlight 
that’s getting a new wire should be tied back into the other headlight at the socket, so that both of these skinny little 
wires are serving one headlight. 

This type of reconnection requires popping the spade terminal out of the headlight socket, soldering the second wire to 
it, and snapping it back into the socket.  Each spade terminal has a little tang on the back that holds it into the socket, so 
you need to insert a pointy object between the plastic and the terminal itself to depress this tang to remove the terminal. 
 You will also want to bend this tang back into position before pushing the terminal back into the socket, so it securely 
snaps into place. 

Of course, when done changing which fuse serves which headlamp you will probably need to revise the fuse sizes in 
the headlamp fusebox.  It’s easy enough to divide the wattage of each headlight by 12 volts to determine the amps that 
it will draw, and install a fuse suitably sized to serve. 

On the other hand, it might be easier to forget all that fiddling with the original fusebox and wiring and simply remove 
the fusebox in entirety and throw it away and run wires directly from the relays to the headlights with inline fuses, and 
install an inline fuse for the electric fan.  If your car is old enough to have the round tube fuses, this isn’t a bad idea; 
those things make lousy connections and are always corroding and getting intermittent.  The later style fuseboxes with 
the plastic fuses are better.  You could, of course, install a generic fusebox that serves all your new headlight and fan 
wiring for a neat installation. 

Be sure to provide adequate ground wires on the headlights as well.  That’s easy to do, by either adding additional 
wires or just replacing the ground wires entirely and connecting the new wires to a screw into the chassis, of which 
there are several handy right around the headlights. 

 
 

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While relay installation may involve a couple hours of fiddling, it is a very cost-effective improvement.  The relays 
themselves typically cost less than five bucks each, and wire and fuses are also cheap. 

 

RELAY INSTALLATION -- SIMPLER VERSION:  Mark Barker provides a simpler method of improving the power 
supply to headlights on his web site.  Rather than using separate main and dip beam relays as described above, Barker 
installs a single relay in the wiring to the OEM main/dip beam relay.  “Unplug the thick blue wire in the middle of the 
dip/high relay.  This now goes to one of the new relay's coil tags; the light switch only has to operate this relay now.  
Thick brown wire all the way from the main bus on the firewall, (under 14mm AF nut, using a ring tag) to one of the 
new relay's closing contact tags.  Another short piece of brown wire from the new relay's other closing contact to the 
exposed tag of the dip/high beam relay the blue wire came from, using the appropriate crimps.  Finally, a piece of black 
wire from the other coil tag to a nearby earth, using a ring tag.”  Ed. note: actually, you might want to make that short 
piece of brown wire a short piece of blue wire to keep the color coding consistent. 

This single-relay method is clearly simpler to implement than the multiple-relay method described above.  Both 
methods eliminate routing the heavy headlight current through the headlight switch on the dash and out to the front of 
the car through the OEM wires, which is the portion of the circuitry where the lion’s share of the voltage loss occurs.  
The single-relay method continues to run the heavy current through the OEM main/dip relay and all the OEM wiring to 
the headlights beyond that, which unfortunately is still pretty skinny.  Also, there’s no convenient way to divide the 
load for two relays, so if the total headlight load approaches or exceeds 30A it would be a good idea to find a relay 
that’s rated for higher current.  Altogether, this option might be advisable only for those who want full power to stock 
headlights, while those intending to install high-wattage bulbs (especially four of them!) might be better advised to use 
the multiple-relay scheme above. 

The single relay only closes once when the headlights are turned on, so the relay itself may last longer than the ones in 
the multiple-relay scheme that open and close whenever the driver switches from main to dip beam and back.  The 
main/dip relay costs a lot more than a couple more generic relays, though, so the multiple-relay scheme may be cheaper 
in the long run due to increasing the life of the main/dip relay -- especially if high-wattage bulbs are used that exceed 
the rating of the main/dip relay contacts. 

 

SO YOU ALREADY HAVE RELAYS:  Sometime in the early 90’s Jaguar got wise and provided headlight relays 
from the factory.  If you own such a car, you don’t have to worry about the headlight wiring.  Right? 

Maybe not.  As discussed above, the purpose of installing relays is to provide the most direct connection to the 
battery/alternator possible using heavy wires to minimize voltage losses.  The Jaguar factory relays may take the long 
routes through the dash switch out of the circuit, but that doesn’t mean they’re using adequate size wire.  Daniel Stern 
says, “I have yet to encounter the vehicle with truly adequate wiring from the factory.  Best I've seen is "passable", and 
that is rare.” 

Wires to individual headlights should be 12 gauge, and wires that power two or more headlights should be 10 gauge or 
larger.  Before you decide your wiring is fine, you might want to check what gauge wire Jaguar decided to connect 
those relays up with.  If the wires from the main bus to the relay contacts and on to the headlights themselves is is still 
the 18 gauge stuff they use for nearly everything else, there is room for improvement there.  You can either rip that stuff 
out and install adequate wire in its place, or you can simply add wires in parallel to the existing wires.  And don’t forget 
the ground wires to the headlights. 

Such work is likely to help the stock headlights considerably, but it is even more important if you decide to install high-
wattage headlights. 

 

UPGRADING HEADLIGHTS -- LEGAL CONCERNS (US):  Before considering any headlight upgrades, it might 
help to know a little about the evolution of headlight laws here in the US.  David Berman says, “In the 1920s and 1930s 
cars did not have sealed beams, they had headlamps with reflectors, lenses and replaceable bulbs similar to today.  
However, they had a serious problem with oxidation of the reflectors which dimmed the lights, and no amount of bulb 

 
 

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replacement (which US drivers did regularly!) would help.  Sealed beams were standardized in the US in 1939 and 
solved the problem entirely by eliminating the opportunity for reflectors to oxidize.  They were such an improvement 
that sealed beam retrofit kits were made for earlier cars, even for the Ford Model A which had gone out of production 
in 1931.” 

By the 1950’s and 60’s, laws had been established requiring all cars in the US to have one of two types of sealed beam 
headlight systems: two 7” round headlights or four 5¾” round headlights.  It was this requirement that ruined the 
appearance of the Jaguar XJ6/XJ12, designed to have two 7” bulbs plus two 5¾”; for the US market, the two 7” had to 
be replaced with 5¾” with a filler ring around them.  It also is the reason the early US-spec XJ-S has two round 
headlights on each side instead of the “Euro-style” oblong single lamp assemblies. 

DOT also limited the light output of headlights on both high and low beam.  The headlights also had to have three little 
bumps on the front, used to check alignment.  On top of all this were general prohibitions on more than four headlights 
or six head/auxiliary lights on a car. 

Sometime in the 60’s they prohibited glass covers over the headlights.  This changed the appearance of the Jaguar E-
type and the Volkswagen Beetle. 

In the early 70’s, they added two arrangements of rectangular sealed beam headlight systems to the approved list. 

With the advent of energy conservation concerns, the automotive manufacturers were finally able to convince US 
legislators in the mid 1980’s to drop the requirements for using standardized sealed beam headlights and permit the use 
of “composite” headlight assemblies in the name of better aerodynamics.  These headlights have a lens/reflector 
assembly that was custom-designed for the car (and usually atrociously expensive), and the bulb itself is a smaller 
quartz-halogen item that plugs into the reflector from the rear.  Berman:  “Given the serious reflector problems in the 
1930’s and the dramatic improvement wrought by sealed beams, you could hardly blame the DOT for taking a long 
time to be convinced that the proposed new generation of reflectors wouldn't become oxidized and therefore the sealed 
beam requirement could be lifted.” 

Unfortunately, apparently the US DOT couldn’t be convinced to legalize the same composite headlights that had been 
successfully used in Europe and everywhere else in the world for decades, so the US-spec cars got their own style of 
composite headlights.  To this day, to be fully legal in the US, your headlight lenses need to say “DOT” on them.  And 
most US-spec headlights seem to still have three little bumps for alignment even when the front of the headlight is 
sloped so some bumps are actually rearward from others.  There are still limits on light output. 

I dunno what DOT’s priorities are, but it’s obvious that they don’t include providing good visibility at night or in rain.  
Not to put too fine a point on it, DOT-spec headlights suck.  And just to show that this is not a “grass is greener” thing 
where everyone thinks people somewhere else have it better, John Warr from the UK says, “You guys in the US have 
to drive with the most appalling lights I have ever come across.  To someone used to Euro lights, the first experience of 
US lights at night in the rain results in a puzzled driver standing in front of his hire car trying to work out what he has 
not turned on.” 

 

E-CODE:  While the US DOT conspires to keep drivers in the dark, the European standards for headlights have 
evolved based on input from major headlight and driving light manufacturers in an attempt to provide truly excellent 
lighting.  Headlights meeting these “E-code” standards are indicated with a capital letter E and a number with a circle 
around it on the lens.  According to Daniel Stern, the number indicates the country in which the headlight was certified 
to meet the code. 

There are E-code headlights designed to replace any standard sealed beam used in the US, and they always seem to 
have a distinctive pattern on the lens: there is a trapezoidal area between the center of the lens and the edge on the 
driver’s side, with the fluting at an angle.  These lights have a distinctive pattern on dip beam, sending light down to 
both sides and up towards the side of the road but not up towards oncoming traffic. 

Stern maintains a site on the WWW that, among other things, describes the advantages of E-code headlights over DOT 
headlights in considerable detail: 

 

 

http://lighting.mbz.org/tech

 

 
 

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Before jumping in and upgrading your headlight system, you might want to check the regulations in your state.  Or, you 
might wanna simply note how few citations are handed out annually for illegal E-code headlight assemblies and decide 
whether or not you wanna chance it.  Stern says, “The fact of the matter is that back in the '70s when all cars had 
sealed beams, E-code lamps stuck out like sore thumbs.  But today, with the proliferation of so many different 
headlamp designs, together with the elimination of headlamp inspections in at least 48 states, nobody knows or 
cares what kind of headlamps you're running.”  So, what’s the bigger risk to you: getting a ticket, or being unable to 
see where you’re going after sunset? 

Stern also notes:  “If you live in the US states of Oregon, Washington, Alaska or Massachusetts, or in the great 
nation of Canada, then E-code lamps are 100 percent legal.” 

Note that many of the “H4 headlights” sold by J. C. Whitney (page 691) are actually low-end E-code units and are 
described as “for off-road use.”  That is how they can sell headlights that are technically prohibited on public highways 
in the US; why the upper left cutoff on low beam would be helpful in an off-road application is never explained. 

There are a couple other tricks that have been used; when “sealed beam” headlights were required, J. C. Whitney sold 
some “sealed beam H4” headlights; the rubber boot had been glued on over the bulb socket making the whole thing 
sealed.  When the H4 bulb burned out, you just cut the boot away and put in a new bulb. 

 

LEGAL CONCERNS -- JAPAN:  The author is no expert on Japanese automobile regulation, but it is clear that there 
are some legal issues involving headlights.  According to the H.E. Parts Catalogue ©1987, Japan-spec XJ-S’s up to 
VIN 118583 (1986) used unique oblong headlight assemblies and unique headlight bulbs.  From VIN 118584 on, 
Japan-spec cars used the same headlights as other RHD countries.  Mike Morrin says, “Interestingly, the 1980 parts 
book shows the Japan market having US spec headlights (including LHD sealed beams!!)  I presume the actual lamp 
units were replaced with Japanese ones on arrival in Japan.”  Maybe not; Japan reportedly got a lot of US cars shortly 
after WWII -- largely from American occupants bringing them over for their own use -- and apparently set up its specs 
to permit use of American LHD cars on its roads where people drive on the left. 

Several people, including Daniel Stern, confirm that the pre-1986 Japanese headlights were really bad, comparable to 
the US sealed beams in their ineffectiveness. 

If you have a pre-1986 Japan-spec XJ-S, you might want to consider upgrading it to the UK-spec headlights which are 
apparently legal there now.  Or you can consider the other upgrades mentioned in the following sections, but be sure to 
check the local regulations first. 

 

SOCKET MELTING:  One possible problem with high wattage bulbs is melting of the plastic socket that plugs onto 
the back of the headlight.  The solution to that problem is easy: remove the socket and install the spade connectors 
individually.  One idea might be to push the spade connectors all the way through the socket and out the other side 
before connecting to the headlight; that way, the wires going through the socket would clearly indicate which spade 
connector goes to which terminal, but the plastic socket itself would remain dangling on the wires a few inches away 
from the headlight. 

 

Four Round Headlights -- US through 1991 

 

The four round headlights used on the US-spec XJ-S up through 1991are sealed beam halogens, available at any auto 
parts store.  The outboard units (sealed beam 5¾” round halogen main/dip 35/35 watt

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) are H5006, and the inboard 

(sealed beam 5¾” round halogen main 50 watt) are H5001.  And yes, I have listed the correct wattages for these units, 
despite the various Jaguar literature listing the outers as 37.5/50 or 37.5/60.  The non-halogen equivalents for the 

                                                

 

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  When listing wattages of high/low beam headlights, I endeavor to list the main beam wattage first, the low beam 

wattage second.  The J. C. Whitney catalog often lists them the other way around.