Reversing Polarity on battery - car now dead!

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Hi,
This is slightly off LC topic, but hoping that someone here might have
some pointers before I start ripping the car apart.
My neighbour was having problems starting their Isuzu Trooper so tried
jum starting it, BUT initially they ended up with the jump leads the
wrong way around.
Now the car is completely dead - there is some power in the battery,
but none of the dash lights are lighting up.
I've been working through the fuses but can't see any blown ones.
I am about to start tracing the main wiring from the battery, but am
wondering if anyone else has come across a similar situation and have
any useful suggestions.
I'm wondering if something has blown in the alternator.
The only relevant bit is was that they were trying to get the car down
to me to replace a Milners starter motor that I put on last December
and it now on it's way out - Milner have immediately sent a replacement
and will pick up the old one once I have got it off.
--
Regards,
Julian Voelcker
Skype: julianvoelcker
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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Julian,
I assume you've already tried to start it with a fresh battery after
disconnecting the alternator, haven't you?
Could it be a spike that knocked down the engine computer (if it's there)?
--
Rgds,
Roman (London, UK)
'92 HDJ80 (auto)
On 8/17/07, Julian Voelcker <[Email address removed]> wrote:
 
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Guest
Hi Roman,
Not yet, been distracted by other things.
I've got the battery out and recharging - it was showing only 11 volts.
However the car was dead when they reconnected the jump leads the right way
around.
When I go back out I'm just going to check the main wiring first before
trying another battery
Possibly, although that doesn't account for all the electrics being down -
no dash light with the ingnition on, etc. I think it is something more
fundamental.
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Skype: julianvoelcker
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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Guest

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Julian,
IMHO reverse polarity could not affect DC devices like motors or
relays. Have you also checked any fusible links between the battery
and the fuse box?
--
Rgds,
Roman (London, UK)
'92 HDJ80 (auto)
On 8/17/07, Julian Voelcker <[Email address removed]> wrote:
 
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Guest

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Don't forget some relays have a "blocking" diode to prevent EMF damage to
contacts when the circuit opens. Mostly used for reed switches etc. I
imagine those diodes will be conducting not blocking is the battery is
reversed, that said the diode is in parallel with the coil so even if it is
fried the relay should operate.
On a really modern vehicle I hate to think what the consequences might be -
my Crossfire supposedly has a CAN bus comms system between the Main ECU,
ESP/TC ECU and other major items. Also most everything goes through a
computer on the car so a motor not operating in the Crossfire would probably
because a chip was toast.
Malcolm Bagley
Stafford UK
FJ45 '75 & FJ45 '76
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13:46
 
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Julian
If you get no power at all anywhere - no side-lights, hazard lights,
interior lights, radio, etc - then it has killed the cabling from the
battery, and you are looking for something melted or a fusible link
gone.
If it's just ignition-on related stuff then my guess would be a fuse -
if they are lucky. There is an Isuzu owners' club:
http://www.itocuk.co.uk/ and I also found some online wiring diagrams at
http://www.autozone.com/az/cds/en_us/0900823d/80/18/46/17/0900823d801846
17/repairInfoPages.htm
That page suggests that some Troopers at least have fusible links - see
the link under "chassis electrical" on the RHS of the page. The picture
seems to say that they look a bit like fuses, rather than the wires we
have on the LC.
It also says this about fuse-boxes:
"The fuse box on most models is located on the lower left-hand side of
the instrument panel or under the instrument panel near the steering
column. There is usually a relay box with additional fuses located near
the battery or on fenderwell."
Good luck!
Christopher Bell
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Hi Julian,
I would go with fusible link, could be located in the wiring harness or
possible in the relays?
Done this on my Honda Accord once and it was a relay instead of a fusible
link, although I don't remember everything being dead?
Not that I am a mechanic I work with computers and that's not ECU's:).
Martin.
Snipped.
 
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Hi Roman,
Managed to track the problem down - a 80am fuse buried behind a cover
in the main fuse box in the engine bay - no indication that it was
there, just came across it whilst pulling the fuse box apart to trace
the wiring!
Fortunately LCs aren't so devious ;-)
--
Regards,
Julian Voelcker
Skype: julianvoelcker
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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Guest

Guest
Julian,
Good. Job done. The battery, however, may need checking under load
with a carbon pile tester.
--
Rgds,
Roman (London, UK)
'92 HDJ80 (auto)
On 8/17/07, Julian Voelcker <[Email address removed]> wrote:
 
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Guest
Julian.
I would check out the alternator. Reversed polarity will toast an alternator quicker than anything and the symptoms are the same as you get when you drown the alternator for too long when wading. A lot of the dash indicators are not driven by the main ECU. May have lost a fuse link as well but pretty sure rhe alternator will be FUBAR.
Cheers
Andy
Andy Harvey
Cheltenham, Glos.
07761 266676
 
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Guest

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Polarity on its own won't blow a fuse, there had to be load that drew 80A+, but only in reverse polarity? Sounds like a diode. I wonder if the rectifying diodes in the alternator do than with reverse polarity? Wouldn't have thought so but would have to think too much to check that on Saturday morning. If the fuse went the alternator might be OK - or might be damaged by hiding it, something to keep an eye on.
Malcolm Bagley
Stafford UK
FJ45 '75 & FJ45 '76
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.5.476 / Virus Database: 269.12.0/957 - Release Date: 16/08/2007 13:46
 
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