Faulty Alternator? No, faulty earth!

I had a problem with a flat battery on my Fabia Mark 2 Hatchback (2012), so I called the RAC and got a jump start.

I was just about to go for a half hour drive along the motorway to recharge the battery when lights started flashing on the dashboard and the mechanic checked the electrics to find that the alternator was only putting out half the power it should 😮

He put a volt meter on the battery which said 14 volts, but then tried it on the engine and got a reading of only 13 volts, the volt drop test indicating that there was a resistance in the electrical circuit.

It turned out that the actual problem was that, at some point, someone had undone the earth connection on the left side of the engine (opposite side to the battery), but then bodged the bolt back on and crossed the threads so it wasn't fully tightened 😒

This resulted in the connection getting corroded and the rust causing higher than normal resistance in the circuit such that the bolt was actually getting hot!

To fix it, since the bottom part of the bolt is (I think) M10, but the top is M8, he borrowed my Dremel and reamed out the hole in the earth cable to let him secure it with the M10 part of the bolt and, once it was back in place, all the parts of the circuit were registering the same voltage.

So thumbs up to the RAC guy for spotting this and saving me having to fork out for getting a new alternator fitted! 👍

I hope this might help someone else who has a similar issue 🙂