[xj-s] 1988 XJS Short drains battery

I have been trying to locate a short that drains my battery after
the car sits for a few days. The car has a new alternator and
battery. It charges o.k. while driving. I have narrowed it to the
number 2 and 3 fuses in the main fuse panel. I have been using a
test light inline with the negative side of the battery to see what
circuits have power with the ignition off. (all lights etc.
disabled) When I pull the fuses the light goes out. If I plug the
number 2 fuse in, the light comes on. It also will occasionally
come on with the #3 fuse in place. Somehow the two fuses seem to
be acting on the same circuit. I have removed the inline fuses
(aerial) and various relays. No luck yet. Does anyone have any
suggestions?–
PGAW
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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1 Like

At 03:43 2003-10-28 +0100, PGAW wrote:

battery. It charges o.k. while driving. I have narrowed it to the
number 2 and 3 fuses in the main fuse panel. I have been using a
test light inline with the negative side of the battery to see what
circuits have power with the ignition off. (all lights etc.
disabled) When I pull the fuses the light goes out. If I plug the
number 2 fuse in, the light comes on. It also will occasionally
come on with the #3 fuse in place.

MAIN #15 (3A) = Trip Computer

Requires a nominal current for maintaining memory and operating the clock
function.

MAIN #2 (7.5A) = Hazard warning, seat belt logic.

Passive seatbelt relays might be partially energized - are the switches
positively actuated? Search the archives.

MAIN #3 (15A) = Clock (!), Aerial, Caravan, Boot Lamps (you know, the thing
that is open while you’re running tests - are you sure they’re disabled?).

For that matter, do you know the boot lamps shut off when you close the
boot lid? Knowing that when you press the button they go out, doesn’t mean
that the button is sufficiently pressed when you close the boot.

If you have an aftermarket stereo, who knows how it was wired in. you
could pull the trip computer and the stereo connectors (behind the
respective devices) and see where your mystery draw is. I much prefer to
use an inline ammeter to take a precision measurement.

Suggestion: pull these fuses and leave them pulled for a couple of days
('cepting the #2, which you can connect when driving, then remove again),
and see if your battery drain magically stops. If it does, connect one and
continue the experiment - if the battery doesn’t drain on that, then the
other circuit is suspect (but go ahead and confirm).

— '88 Jaguar XJ-SC 5.3L V12 (LHD) ‘Black Cat’
Sean Straw '85 Jaguar XJ-S 5.3L V12 (LHD) ‘Bad Kitty’
Marin County, California '91 Jaguar XJ40 4.0L (LHD) ‘Trevor’
http://jaguar.professional.org/ '69 Buick GranSport 455 V8

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In reply to a message from PGAW sent Tue 28 Oct 2003:

How long should our XJSes be able to sit before the battery is
drained - a week, 2 weeks, a month?–
The original message included these comments:

I have been trying to locate a short that drains my battery after
the car sits for a few days. The car has a new alternator and


&:-)) Paul '88 XJ6 VDP 130k & '90 XJS coupe 127k
Garland, Texas, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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Depends on the year model, I suppose. Mine, sans trip computer etc.,
can easily last for a month at least.

Ed Sowell
76 XJ-S

How long should our XJSes be able to sit before the battery is
drained - a week, 2 weeks, a month?

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Mine (with trip computer) has lasted up to 6 weeks, but it only just
started. In cold weather, I’m sure it would not have. So I think 4 to
6 weeks is about the max.

John Rickman
Melbourne
'88 XJ-S V-12 Coupe

Ed Sowell wrote:

Depends on the year model, I suppose. Mine, sans trip computer etc.,
can easily last for a month at least.

Ed Sowell
76 XJ-S

How long should our XJSes be able to sit before the battery is
drained - a week, 2 weeks, a month?

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