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Jump Leads The Wrong Way Round

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#1 1998CooperSport


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Posted 03 February 2019 - 01:14 PM

Hi all,


I have a 1998 Rover Mini Cooper Sport (1275cc). Battery died over the last couple weeks not running it, tried to jump start it today. It was dark, and my neighbour's battery does not have a colour indication of which is + and -, and the jump leads were the wrong way around. Horn blasted and some smoke came out of the bottom.


I took the leads off, tried jump starting the right way round, it started and sounded fine but immediately died when the jump leads were disconnected. I checked the fuses by the driver's seat and they're all fine. I'm not sure how to check the fusible relays in the engine compartment.


How much damage could have been done? What's the most likely fault?


Thanks all. And yes, I do feel like an idiot.

#2 wile e coyote

wile e coyote

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Posted 03 February 2019 - 01:46 PM

It happens! I did the same to jnr's lupo in similar circumstance - and blew the alternator rectifier / diode.- so I'd rather suspect that you may have done the same which may make sense if your battery is dead as a dodo - if the alternator's dead then no engine driven charge to keep the spark going - I don't pretend to understand the workings of alternator components - someone far better educated will doubtless be along soon, but it seems you can get a replacement rectifier for the Lucas ACR alternator for about 15 quid......far cheaper than a new unit


Smoke came out of where exactly? Before attempting any further starts, charge your battery up off the car, see if it still holds charge / 13v &  check the wiring thoroughly, hopefully no damage! and have someone on standby with eyes peeled and an extinguisher to hand

#3 smudger068


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Posted 03 February 2019 - 03:26 PM

Being really optimistic but could the battery have not had enough charge in it in the first place when you disconnected the leads? What voltage does the battery have before you jumped it? Is your alternator actually putting any voltage out?
There is a reason why your battery died in the first place, what is that reason?

Edited by smudger068, 03 February 2019 - 03:28 PM.

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