Battery connected wrong way - How much damage?

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39
Location
Wessex
Hi all,

Went to move my SIII 109 diesel, and [stupidly] touched the leads onto the battery terminals the wrong way round. Obviously there was a loud bang and some sparks, and I quickly took the leads off. However, since this incident there is now a dead short across the positive and negative leads, with no current and a resistance of 99 Ohms on a multimeter readout across the 2 leads with the battery disconnected, The battery itself is fine, as are all 4 fuses, but there is now a battery-draining short circuit which prevents the vehicle from starting. The ignition was off at the time if that helps.

How much damage have I done? What do I need to check?
 
+1 on likely damage to the rectifier / regulator in the alternator...
You say there is a dead short across the leads, but then you say that the resistance measurement is 99 Ω.
99 Ω would indicate a very low discharge rate (~1.5W), not a dead short?
As you are talking about diodes in the circuit, you might get a different resistance reading if you connect the meter the other way round.
Anyway, first step is to disconnect the alternator as above...
 
+1 on likely damage to the rectifier / regulator in the alternator...
You say there is a dead short across the leads, but then you say that the resistance measurement is 99 Ω.
99 Ω would indicate a very low discharge rate (~1.5W), not a dead short?
As you are talking about diodes in the circuit, you might get a different resistance reading if you connect the meter the other way round.
Anyway, first step is to disconnect the alternator as above...
Alternator +2.....anything electronic ie radio if switched on or maybe its permanently on.....and other electronic gadgets.
 
Thanks everyone, I have disconnected the alternator, the engine now starts and everything works perfectly. The multimeter shows an open circuit with the battery terminals disconnected. I'll have a look at fixing the alternator, if not then I'll have to lighten my wallet :eek:
 
Thank your lucky stars you dont have a more modern car with an ECU ect ect.....you could now have a bill exceeding £1000.

Exactly the same will happen if you connect jump lead back to front......£££££££££££££££££££££££££££
 
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