So I was approached in a car park this morning by an old chap asking if I could give his fiesta a jump start. Was feeling helpful so agreed. Moved my car to by his, bonnets opened and he grabbed his jump leads. So far, so good.

So I took the positive clamp from one end of the jump leads, nothing else connected or touching anything, and went to connect it to the + post that goes though the scuttle/bulkhead in front of the battery. As soon as it touched the terminal, huge sparks and my car died

Obviously, first thoughts were "crap, how many expensive electronics have just shorted and been killed", and "how the hell did that happen?"

Went to the driver door, interior lights on, stereo still running etc. Went for a restart and it started right up, and seemingly no ill effects.

But how did it happen?! Nothing connected to the fiesta, jump cable clamps not touching each other or anything else metallic, all I did was go to attach the positive clamp of one end of the jump leads to the + post on mine.

Needless to say, after that, I suggested he went round the corner to the garage and borrowed a booster pack! 2004 Vogue TD6 - Remapped
2008 Porsche Cayenne S
1998 Lotus Elise

Are you sure the other ends of the jump leads weren't touching each other? Current:
- 2017 L405 3.0 V6 Autobiography
Sold:
- 2013 L405 4.4 TDV8 Vogue
- 2004 L322 4.4 Vogue (BRC LPG)
- 2002 L322 4.4 HSE (having fixed timing chain guides)
- 2000 P38 4.6 Vogue (BRC LPG)
- 1981 2-door In-Vogue
- 1980 Ex-Army SIII LWB
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- 2003 L322 4.4 Vogue

Is the insulation on your jump lead ok? No nicks or worn patches where the conductor could have earthed itself.

You are certain that the battery connector is properly seated? That you didn't loose connection to the battery for a second while connecting the leads? This happened to me. Worn posts on the battery, and the clamp doesn't allow for much deviation before it bottoms. 2007 L322 3.6 TDV8 Stornoway

id say you've hooked them up wrong and blown one of the big fuses somewhere

'As soon as it touched the terminal, huge sparks and my car died'

Can you explain what you meant by 'my car died'?

This is the thing, I had the positive clamp in one hand and the negative in the other. Other guy was holding the positive and negative clamps at the other end of the leads. Only clamp that made contact with either car was the positive at my end. 2004 Vogue TD6 - Remapped
2008 Porsche Cayenne S
1998 Lotus Elise

WB, by car died, engine immediately cut out 2004 Vogue TD6 - Remapped
2008 Porsche Cayenne S
1998 Lotus Elise

Bembo449, yeah I expected at the least a major fuse to have blown. But nothing blown, started right back up again and everything works normally. 2004 Vogue TD6 - Remapped
2008 Porsche Cayenne S
1998 Lotus Elise

When jump starting the supplying car engine should remain off until both cables are securely attached. Then the supplying car should be started followed by the receiving car.

I don’t have a clue of the technicalities but possibly a failsafe may have kicked in on your car to avoid damage from a voltage drop when you connected the other car.

Another factor is the RR batteries are high Amp and if the jump leads were not heavy duty (high Amp that may also be an issue.

WB, valid points. Though in fairness done many a jump start in my time, admittedly not with the RR, and always had the supplying car running while connected. Always connect in order of supply car +, flat car +, supply car -, flat car -.

These were the other guys jump cables, but seemed and felt heavy duty, not the crappy thin jobs.

Everything said, other guy was stood there at his end of the cable, positive clamp in one hand, negative in the other. I had negative in one hand and was connecting the positive in other hand to mine. So no circuit could be made, which would lead to the obvious short.

Just damn weird! 😲 2004 Vogue TD6 - Remapped
2008 Porsche Cayenne S
1998 Lotus Elise

As mentioned, check your terminals. Connecting a jump lead to one post with non other connected, cannot cause anything.

Click image to enlarge

I was always told not to have the engine running when you're trying to jump start another car as you risk killing your alternator as it's not rated to supply the current being drawn.

This may well be out of date advice, but I never risk it. 2010 4.4 TDV8 Vogue SE