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Car Forum / Jaguar Cars / June 2005

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XJS Electrical... how to diagnose

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WayneC - 05 Jun 2005 02:35 GMT
On my 84 XJS, the circuit that includes the instrument panel and reverse
lights keeps blowing it's fuse, although I can't seem to ever catch the
exact moment it happens.... ie, I put a new fuse in and it may last a
half hour or a few days before I notice that the instruments have
stopped working again. I tried putting a new reverse switch on the
shifter, but that didn't fix the problem, nor can I pinpoint the fuse
blowing at the same time the shifter is used.

In retrospect, I have had a nagging electrical problem for many years
with this car, in that it would run the battery down if it sat more than
2 or 3 days without being driven; I had it in the shop several times for
this, and they removed the anti-theft system and disconnected the cigar
lighter, among other things, but the problem persisted. I got tired of
throwing money at the problem so I installed a battery disconnect switch
to use whenever I knew I wouldn't be driving the car for awhile.

Now recently I have this problem with blowing the fuse, and,
interestingly, the last time I parked the car it had a blown fuse again,
and I forgot to shut off the battery disconnect switch; it sat several
weeks, and the car started right up (no battery drain!)... so I'm
thinking whatever is blowing the fuse may be the same problem as the
battery drain problem (or may not, I suppose).

Anyone have any ideas on how I can track down this/these problem(s)?
Neil - 07 Jun 2005 09:05 GMT
do you have a tow bar??? could be some bad wiring in the tow bar electrics.

> On my 84 XJS, the circuit that includes the instrument panel and reverse
> lights keeps blowing it's fuse, although I can't seem to ever catch the
[quoted text clipped - 20 lines]
>
> Anyone have any ideas on how I can track down this/these problem(s)?
WayneC - 07 Jun 2005 22:07 GMT
> do you have a tow bar??? could be some bad wiring in the tow bar electrics.

No, no tow bar.
Chris Booth - 07 Jun 2005 17:17 GMT
Check the junction of the wiring loom & the dash/ignition circuits ( 2 large
plastic connection blocks) for corrosion.
Had similar experience cost around £400 in towing fees & £300 to fix the
mess the breakdown guy made of the wiring!

chris b (XJ40)

> On my 84 XJS, the circuit that includes the instrument panel and reverse
> lights keeps blowing it's fuse, although I can't seem to ever catch the
[quoted text clipped - 20 lines]
>
> Anyone have any ideas on how I can track down this/these problem(s)?
Vlad - 07 Jun 2005 20:10 GMT
Jaguars are famous for electrical problems

I am not familiar with your particular  model ( I have a 78)  but to
find the problem I would remove the fuse and  connect a "sonalert" or
any type of buzzer to the opposite of the supply side.

Then insert de fuse and move all harness and the accessories that are
connected to that fuse. When the buzzer stops buzzing, you know you
have found the problem

If you have more that one wire connected to the non supply side of the
fuse, you could also insert individual fuses and this way get a better
idea on the location of the problem,

You can also replace the fuse with a 12Volt bulb (high current) and
move things around . When the brightness of the lamp changes you know
where the problem is.

In any case, intermittent problems are hard to trouble shoot and in a
Jaguar are certainly not  an easy task.

In certain rare cases when a destructive process is allowed I have
placed a much stronger fuse and look for smoke. I am not recommending
this.

Vlad


>Check the junction of the wiring loom & the dash/ignition circuits ( 2 large
>plastic connection blocks) for corrosion.
[quoted text clipped - 27 lines]
>>
>> Anyone have any ideas on how I can track down this/these problem(s)?
WayneC - 07 Jun 2005 22:27 GMT
> Jaguars are famous for electrical problems
>
> I am not familiar with your particular  model ( I have a 78)  but to
> find the problem I would remove the fuse and  connect a "sonalert" or
> any type of buzzer to the opposite of the supply side.

Interesting thought... but probably what I need is something that will
start making noise when the power ceases (fuse blows) so I can figure
out if something in particular is happening at the time it blows.
Something like those old aftermarket buzzers that warn you when you've
turned the ignition switch off but left the headlights on.

> Then insert de fuse and move all harness and the accessories that are
> connected to that fuse. When the buzzer stops buzzing, you know you
[quoted text clipped - 3 lines]
> fuse, you could also insert individual fuses and this way get a better
> idea on the location of the problem,

Another interesting thought.

> You can also replace the fuse with a 12Volt bulb (high current) and
> move things around . When the brightness of the lamp changes you know
> where the problem is.

Or maybe add a light to the circuit and put it on top of the dash.

> In any case, intermittent problems are hard to trouble shoot and in a
> Jaguar are certainly not  an easy task.
[quoted text clipped - 37 lines]
>>>
>>>Anyone have any ideas on how I can track down this/these problem(s)?
Vlad - 08 Jun 2005 00:17 GMT
>> Jaguars are famous for electrical problems
>>
[quoted text clipped - 7 lines]
>Something like those old aftermarket buzzers that warn you when you've
>turned the ignition switch off but left the headlights on.

That is what a Sonalert is. They use to cost about $5.00 but today you
can get a buzzer 3 small batteries and a microswitc for a dollar . I
know, I just purchased 4 of them at the local dollar store.

>> Then insert de fuse and move all harness and the accessories that are
>> connected to that fuse. When the buzzer stops buzzing, you know you
[quoted text clipped - 11 lines]
>
>Or maybe add a light to the circuit and put it on top of the dash.

Yes , why not?

>> In any case, intermittent problems are hard to trouble shoot and in a
>> Jaguar are certainly not  an easy task.
>>
>> In certain rare cases when a destructive process is allowed I have
>> placed a much stronger fuse and look for smoke. I am not recommending
>> this.

>> Vlad
>>  
[quoted text clipped - 30 lines]
>>>>
>>>>Anyone have any ideas on how I can track down this/these problem(s)?
 
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