Jaguar XJ-S. Manual — part 147

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Alternative plan B is to forget the stock bracket and simply fashion a bar across the top of the battery. Longer J-bolts
can be used, and two 1/4” holes made in the top of the original plastic cover. Then, after the battery is secured with
nuts and washers, the cover can be installed and additional nuts -- real pretty cap nuts or threaded knobs, they show
within the boot -- can be used to secure the plastic cover.

FYI: the battery compartment in the ’83 XJ-S is 10 inches by 6-3/4 inches. The ideal battery height must be shorter
than 8 inches, terminals included. The height to the flat top of the Champion 78-2 is 7 inches, and it fits with room to
spare. It is highly recommended that you confirm the size of the compartment in your own car before shopping for a
battery; the various documentation on what size battery to use, including those cute computerized battery selector
displays, seem to be wrong more often than they’re right.

One general observation about car batteries and warranties: There are some excellent $60 batteries out there with 60-
month warranties (or longer). However, some $60 60-month batteries are actually a scheme to sell you a $40 battery
every 3 or 4 years; it dies, you bring it in and complain, and they happily install another battery just like it and charge
you the “pro-rated” cost based on how long it lasted -- about $40. If you think about it, you’ll realize they could just as
well claim the same battery is good for 20 years and charge you $240 for it -- you’d still end up bringing it back every
three or four years and paying about $40 for a replacement. The only thing you’re buying by paying more than $40 for
the battery is the “hook” that convinces you to keep buying the same battery rather than trying some other make to see
if it lasts longer. If you buy a 60-month battery and it dies without due cause in far less time, you might be well advised
to simply write off that warranty and buy another make -- unless, of course, you don’t mind having to replace your
battery every 3 or 4 years.

There are some people who select batteries on the basis of cranking amps. The logic works like this: The car only
requires a certain number of cranking amps to start, and almost any battery will start the car when new. However, as
the battery ages, its cranking capacity diminishes with time, until eventually the battery will no longer start the car. The
more cranking amps the battery has to begin with, the more it can deteriorate before replacement is required. This
theory assumes a lot, including that different batteries deteriorate at comparable rates and that the battery doesn’t suffer
other types of failure such as internal shorts. As such, this theory probably doesn’t apply to unusual batteries such as
the Optima, but may be a fairly valid method of comparing conventional batteries.

But to this theory must be added another monkey wrench: In order to maximize cranking amps, the plates within
batteries must maximize surface area, which is done by making them look like grids or screens rather than plates. With
successive charges and discharges, these grids get more and more deformed (metal is etched away when discharging,
plated back on when recharging, possibly in a different place than it was before), possibly reducing the cranking
capacity faster than flat plates would. Also, the grids might fracture more easily with vibrations, causing internal shorts.
There are so-called “rough service” batteries available that go the opposite route: they sacrifice cranking amps in favor
of a rugged plate design that won’t go to pieces if you install it in a truck and drive it across the Baja Desert.

BATTERY TERMINALS: If your XJ-S has the original battery terminals on the ends of the cables in the trunk, the
5/16” nuts used to clamp those terminals down on the battery posts require a 1/4” Whitworth wrench size. See page 24.

BATTERY HOLD-DOWN NUTS: Also Whitworth.

DEAD BATTERY PROBLEMS: If your battery is dead after the car sits for a few days, it’s time to check for current
flow when everything is supposed to be shut off. The standard method for doing this is to disconnect the battery and
reconnect it with an ammeter in the circuit, and monitor the amps as you pull fuses one by one. The current with
everything off should be in the milliamp range; if it’s amps rather than milliamps, you need to find out what’s being left
on when the car is off.

Of course, the first thing you find out is that since the battery is in the trunk, the trunk lights are on while you’re
fiddling in there. So you’ve gotta shut off the trunk lights somehow to continue with the test. It is simply astounding
how often the test doesn’t find a problem -- because the problem was the trunk lights! The trunk lid isn’t securely

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pushing the button on the switch, so the lights stay on with the lid closed. Or sometimes stay on with the lid closed, so
sometimes the battery dies and sometimes it doesn’t.

Craig Waterman fixed this problem by reinstalling the switch with a couple of washers under it to hold it up more.
Others have fixed it by bending the bracket it’s mounted on. The author went a slightly different route to address the
same problem. On the ’83, the flat metal surface on the inside of the trunk lid is supposed to be pressing that button. I
purchased a set of stick-on plastic chair feet from a hardware store and stuck one on. Of course, now I have three spare
chair feet left over. This fix can be viewed at:

http://www.jag-lovers.org/xj-s/book/TrunkLightSwitch.html

Then Stephen Edward Haley noted that on his ’89, adding a chair foot isn’t necessary because Jaguar already did. They
didn’t use a chair foot, of course; they manufactured a special part attached with two screws. Probably cost you half a
month’s salary from your local Jaguar dealer.

Note that the early cars didn’t have this switch at all. They apparently had the more simplistic light bulb in the trunk lid
itself with a mercury switch operating it. So, these cars don’t generally have this problem with the trunk lights killing
the battery.

TRUNK LIGHT CONTROL: On any modern automobile, the trunk lights have a little switch so you can turn them off
when you don’t need them. Jaguar forgot to provide that nicety -- but it’s simple enough to add it. Just purchase a tiny
toggle switch and mount it adjacent to the trunk lid switch and wire it into the same circuit. There’s plenty of room
there, and it’s easy to find in the dark.

AVOIDING A DEAD BATTERY: Scott Jarvis suggests: “You can order a Battery Buddy from Outer Banks, (800)
682-2225, part # batbud. It mounts to the side of your battery and monitors the voltage. When the voltage drops below
a set level, it automatically switches off to preserve the battery. You just reset a breaker and away you go! Many of the
Boating catalogs should carry this and you may find a better price.”

Kyle Chatman responds: “You can also try Priority Start from BLI International, Dept HR12, 17939 Chatsworth St.,
Ste. 521, Granada Hills, CA 91344, 800-780-8276. It monitors voltage drain when the switch is off and disconnects the
battery if it gets too low.”

Ned Blagojevic counters: “This is available in a kit form from Jaycar Electronics (Sydney), kit number KA-1739. The
kit was published in Electronics Australia (Jan 92 issue). It connects to the accessory line and measures line voltage. If
voltage drops to preselect limit between 10.9 and 11.9 it shuts off the flow. The kit includes a relay and specs.”

John Setters provides a different alternative: “Here in NZ an enterprising company called PowerBeat has been formed
to manufacture the answer to starting problems. They have developed an automotive battery which I believe is in two
portions - one section runs the general electrics, the other is reserved exclusively for engine starting. The URL for
PowerBeat is

http://www.powerbeat.co.nz

.”

Sears also sells a battery with a switch on it, so you can switch to a “reserve” and get started.

Fuses and Fuse Blocks

If your XJ-S is old enough to have glass tube fuses, take note: the UK uses a different definition of the rating for these
fuses than the US does. The US rating is for how much current the fuse will carry without blowing; the UK rating is
for the amount of current to blow the fuse within a certain time. The difference is about 2:1. Simon S. Johnson sends
the following data: “...the source: a 1974 edition of “Buss Fuse Car and Truck List” which has on the back cover a

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section call “Foreign Car Fuse Replacement Data,” -- foreign to the US, that is. It states that “English standards differ
from US standards. This accounts for difference in ampere ratings.” Then it provides a list:

English

Type Buss

Replacement

50

amp

AGC

30

35

amp

AGC

25

30

amp

AGC

20

25

amp

AGC

15

20

amp

AGC

10

10 amp

AGC 7 1/2

5 amp

AGC 3

You may find that your fuses have a little paper label inside with both ratings; a Lucas rating (British) and a
“continuous” (American) rating.

If your car uses tubular glass fuses and the ROM specifies an amperage, it’s in the British rating; you will have to
correct per the chart above to use the correct American fuse.

UPGRADING TO PLASTIC FUSES: Older XJ-S’s have glass tube fuses, both in three main fuseboxes and in several
inline locations throughout the car. Later cars have plastic fuses, a type found on many modern cars with the amp
rating clearly marked on the top and color-coded as to amperage as well; these are called ATO/ATC fuses or “blade”
fuses. Now, there are those that will look at the plastic fuses and pronounce them “cheap” -- and they’ll be correct, they
are certainly cheaper to make than the glass tube fuses. But don’t confuse “cheap” with “inferior” -- the plastic fuses
are much better than the glass tube fuses. The small spade terminals make much more reliable connections with the
fusebox than the metal caps on the ends of the glass tube fuses do. And even when the connections are working just
fine on both, the plastic fuses cause less voltage drop in the circuit.

If you are new to Jaguar ownership, you’re probably thinking, “Yeah, right. The glass tube fuses worked just fine in all
sorts of cars for many decades, they can’t be that bad.” If you feel that way, go ahead and skip the rest of this section --
but remember it’s here. You’ll be back.

While you’re pondering the superiority of plastic fuses over glass fuses in general, allow me to point out the superiority
of generic fuse blocks over the OEM fuseblocks in the XJ-S. While the fuse blocks in most cars are something you
never pay any attention to, the fuse blocks in the XJ-S are a known trouble source. This author had troubles with the #1
fuse location in the headlamp fuse block in my ’83, the fuse that serves the small electric fan and the horn. It seemed
that every time I checked, this circuit was not working -- and I got to where I would tap the horn regularly to check.
When it quit, usually the fuse itself had failed -- not blown, but rather had lost continuity within one of the end caps.
Since the small fan was in fact a heavy-duty critter from a Mercedes, I thought maybe it drew too much power, so I
went to a bigger fuse. No help, quickly failed again, again not by blowing but by coming disconnected internally.
Went to a larger fuse still, and the fuse block itself started to melt and issue smoke! A fuse holder should never get hot
-- it should either say cool or the fuse should blow. I decided there was too much resistance in there somewhere and
abandoned this socket. I pulled that pair of wires out of the fusebox and connected them to a plastic 20A fuse. No
further problems.

Unusual problem? Iain Burgess: “I had similar problems with the A/C blower fuse in the main fusebox on my XJ6.
The plastic around the terminals that held the fuse eventually melted, for some reason, the contacts in the fuse box
would heat up, regardless of whether the fan was blowing maximum or minimum. The fuse would eventually fall out
and the blowers would stop working (Lucas's second line of defence??) The fuse never blew. Irrespective of the
current draw, there seemed to enough resistance between the fuse and the contacts to generate enough heat to melt the
plastic. I replaced the fuse a number of times, cleaned the contacts with contact cleaner, sand paper, you name it, but it

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still got hot. I fixed it like you did, replacing that section of the fuse box with an inline spade fuse - no further
problems. None of the other fuses in the box were affected either.”

Donald Neff: “You are on the right track - the heat is caused by the resistance of poor contact. But as you know, since
you cleaned the fuse tabs and holder sockets, it is not the fuse contacts. They are probably the best contact in the
system at any time.

“I'll bet it is the wire-to-fuse holder connection. These are usually poorly crimped connections with no protective
covering. They work fine when new, but deteriorate slowly over time. Eventually the wire collects a high-resistance
coating of oxide between it and the metal of the fuse holder creating a hot resistor at that point.

“I cut the wire back to clean copper and pry the crimp open to remove the corroded section. After cleaning the crimp
tabs I insert the clean wire, recrimp it and then solder it. The solder not only provides more surface area for current
flow, it (crudely) seals the copper from oxidants. It has worked well for me for a few decades.”

Larry Lee talks about his 1979 XJ6: “The S2 fusebox can be the source of a variety of seemingly unrelated electrical
failures, thanks to an interesting design. Several circuits are supplied by one wire from the battery in some cases.
Electricity is supplied to adjacent fuse sockets through the ends of the fuses themselves. Corrosion can be a killer here.
Be sure all of your sockets and the ends of your fuses -- particularly the ends on the "supply side" -- are clean. I had a
glitch involving my A/C and wipers a while back that was caused by this.”

Walter Acker IV points out that it’s not that big a job to replace your old-style fuseboxes with new fuseboxes that use
the better plastic fuses. Obviously, one method for upgrading to the later style fusebox would be to obtain the
fuseboxes used in the later XJ-S. However, this might not be as helpful as one might expect. For one thing, the
electrical stuff apparently changed rather significantly over the years, and the later fuseboxes are likely to have fuses for
components and wiring that didn’t even exist in the earlier cars. Second, when Jaguar changed fusebox styles, they also
changed the mountings, so you may have to do more upgrading than you planned just to get them installed.

The best and easiest solution is to use generic fuseboxes. In fact, Walter Acker IV and this author recommend basically
the same type aftermarket fusebox in particular. One source is

Painless Performance Products

http://www.painlesswiring.com/

Phone: +1

817-244-6898

Sales: 1-888-350-6588

sales@painlessperformance.com

Tech: 1-800-423-9696

tech@painlessperformance.com

This outfit offers several models of fuse blocks, with many having wires pre-attached and even pre-labelled as to which
fuse serves what load, and some even have a relay for providing a switched source without loading up the ignition
switch and existing wiring. But for our purposes, Acker recommends the part number 30002. This is a simple 4-fuse
block, but it costs less than $8 and it has a clever arrangement by which you can assemble blocks together to form an 8-
fuse block or a 12-fuse block or any multiple of 4. It also has no wires connected, just the terminals that snap into the
box, preferred by people like Acker and myself who would rather terminate wires than splice them.

A tip on acquiring such fuse blocks: Painless recommends you buy from their authorized distributors, and one of their
authorized distributors is AutoZone; they don’t stock the Painless items, but will order them for you. But if you just
walk back to the rack, you’ll find the exact same 4-fuse block -- except that it’s made by Conduct-Tite!, part number
115280, and sells for less than $4! Such a deal!

The terminals that are used in these fuse blocks come in a strip of four. Hence, if you’re dealing with one common
power source, you connect one wire and pop the entire strip into the block and go to work on the other four. If you are
fusing four separate power supplies, you merely snip this strip of four into four individual terminals and wire each one
separately and snap them into the block. However, Acker points out that you must be careful not to cut away too much
of the strip. It is the breadth of this strip that prevents the terminal from passing through the block, so if you trim too
much of it away you can end up trying to pull a fuse and getting the terminal and wire coming right out of the block
with it. Just snip about a 1/8” wide section out between the terminals to avoid them contacting each other and leave it
at that.