Reverse polarity - are my electrics knackered?

My M reg K11 1.3 was in need of a new battery, so when I lent my car to my sister she needed to jump start it off of another car. She isn't the most mechanically minded (not that I am either, to be fair) and accidentally connected the leads to opposing terminals and as a result has shorted out the electrics I think. The relay beside the battery is clicking away when the key is turned but there seems to be very little life elsewhere. Before I (or rather she!) has to spend a bundle I was wondering if anyone could give me a run-down as to what is likely to have been damaged, how badly and what I can do to sort this out myself. I'm also really worried that the factory-fitted immobiliser has been shot.

Any info/pointers will be greatly appreciated...
 

Ed

Fusion Motorsport
MSC Founder
Official MSC Trader
depends on how flat the other battery was. If one was really dead and the other very good, its certaintly possible to have done damage.

You need to give us more info on what does or does not work. Example, radio...
 
OP
OP
R
Righto -

Radio light that normally blinks on/off is completely dead.

Immobiliser light that normally blinks on/off is dead.

Tried the headlights; no luck there. But the dashboard indicator that tells you the full beams are on comes on but a bit on the dim side.

Indicators aren't working either.

I'm pretty sure something somewhere has indeed blown.

Apparently the donor battery was in good shape as the lady with the donor car said it was quite new. My battery was on its last legs - hence the need to jump it from another car.

I've been told that there are two fuses under the bonnet beside the battery and that one or both may be blown? One is for one half of the car's electrics and the other is for the other half. Havent had a chance to check this as I'm at work!

Apologies for the vagueness of the above; I'm really not that up on my car knowledge, but I hope to be a bit more after this! If you need more info just post/email me with specifics and I'll do my best. Again, any help GREATLY appreciated.

Tom
 

kennierobo

Buy & Sell Member
if you have joined battery wrong way around then by doing so you have made 24 volts you might have fried some fuses even the alternater the battery however should prove to be okay when re charged overnight......
 

Ed

Fusion Motorsport
MSC Founder
Official MSC Trader
no, he has not made 24v, he would have put 12v backwards through his car. You need to check every fuse. Starting with the larger under bonnet ones first (the ones by the battery)
 

kennierobo

Buy & Sell Member
we used to use two 12 volt batterys wired cross pole to make 24 volts on the wagons, so how is putting jump leads on wrong way not making 24 volts its the same thing..........Series and Parallel Battery Wiring
Lead-acid batteries always have 2 volt cells wired in series to give the desired voltage. Some batteries have 3 2 volt cells in the case, already wired together for 6 volts. Most battery banks use a combination of series and parallel wiring.
Series wiring increases voltage but NOT amp/hour capacity.
Parallel wiring increases capacity but NOT voltage.
 

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frank

Club Member
iv,e got a feeling ed is right , if you connect 2 batterys backwards its like a dead short and more, the good battery will drain the flat 1 then start to charge it backwards to minus 12v, i once put a flat batt on charge the wrong way round and ended up with a minus 12v batt
 

kennierobo

Buy & Sell Member
so when you see wagons with 2 cross wired batterys on they are running - 12 volts..........the wiring in Series and Parallel mean nothing then. when you put a battery on charge back to front it is totally differant than joining two batterys poss to neg this gives you 24 volts not minus 12 volts, if it was minus then there would be no damage think about it.
 

frank

Club Member
prety sure that 2 batterys plus to plus neg to neg is 12v, plus to neg is 24v, but plus to neg AND plus to neg is a double dead short !
 
When you jump start a car you are effectively adding another battery in parallel.
Same voltage but higher ampage. As in Japseye's first image.

Japseye,
I can see your thinking but look at your second image.
The outputs are at each end of the 3 batteries.
To get 24V, you would need car battery neg black connected to earth on the car as normal, then the red +12V from the car battery connected to the neg black on the second battery and the red +12V from the second battery connected to the car's red 12V cable.
 

NeX

You're after my robot bee
Club Member
sounds like you have shafted the battery, try another jumpstart with the cables round the RIGHT way lol
 
OP
OP
R
Got to the bottom of it I think. Checked the fuses under the bonnet and found the 65A fuse blown. I think I need a new battery too. Is it worth buying one cheaply from a scrappers yard or similar? Also, the relay under the bonnet is making strange weird clicking noises when I connect another battery - is this shot as well do you think?

Cheers!
 

Ed

Fusion Motorsport
MSC Founder
Official MSC Trader
I expected to see what you have so far said. Get a new battery and fuse in it. Then start over. Dont bother with an old battery its a waste of time, and new batteries are not expensive anyway.
 
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