The battery is about 3 months old.

The charging voltage is 14.1V to 14.2V at tickover dropping to 13.8 with all electrics switched on.

When engine is started, the charge (battery symbol) light comes on and can take a few minutes to go out. However the alternator whine is as it's always been (a bit louder as it recharges the battery) and the charge voltage is as above.

It's probably a bad connection somewhere but everything looks clean. I've been underneath to check the alternator and all is good.

Can anyone suggest where the wiring fault may be?

It might be the battery even though it's not that old.
If it isn't taking a charge properly, it'll not feed back and cause a light.

You should be able to get the lot tested at Halfords, they attach a tester to the battery that'll test the battery load and alt output.
Though it's worth looking over their shoulder at the results as they do like to sell new batteries.

It's also worth checking the earth straps to the body as well, I believe the one from the engine can rot away.

Thanks, I'll get that done. I'm also fitting a voltmeter as I'm suspicious about the voltage reading ok but the light remains on.

most likely you just need a new or reconditioned alternator.

Or could be the belt slipping.
They usually start to slip when under load after starting.

usually they whine when the belt is too slack... consider trying to tighten it and see if the misbehaviour goes away... (loosen 3 bolts that holds the alternator, tighten the belt, and fasten the 3 bolts again while making sure its very tight)

dac69er said:

most likely you just need a new or reconditioned alternator.

Click to expand...

I hope not but it delivers 14.2 volts (when it does kick in) and battery has not gone flat so I don't believe the alternator has failed.

TobiasBB said:

Usually they whine when the belt is too slack... consider trying to tighten it and see if the misbehaviour goes away... (loosen 3 bolts that holds the alternator, tighten the belt, and fasten the 3 bolts again while making sure its very tight)

Click to expand...

The belt does not feel very tight but it has a sprung tensioner (air conditioning also fitted). There is no abnormal noise from the belt after engine start.

I still need to dig around with the heavy lead from alternator to starter and battery.

Problem solved

Digging about done today.

The thick lead from alternator to starter to battery looks fine. Access is horrible under inlet manifold so I left it alone. The earth tape under the battery was totally hidden so out came the battery and it's case.

Once it was all out (first undo all wiring loom clips and the three M8 Nuts/bolts under the tray) the braided earth strap looked strange at the gearbox end. There was a weird yellow goo soaked into the braid and ferrule. Pulling it out I suspect it was brake fluid. The slave cylinder bleed nipple is broken so there could be a slight dribble leak.

Shops were shut, so I made up a new earth strap from a double length of old jump lead cable.

Once all was bolted back together, the car starts fine (as it always has) but the alternator is humming immediately at 14.2V. Sorted (I believe).

Top tip:
If you need to make a bolt on cable ferrule but don't have the crimp on ends -

Using a non-corrosive flux. Twist the wires and put a dab of solder on the bare ends to keep them tidy. Now wrap the wire around a stainless nut and bolt. Gently tighten the not onto the conductors. You can now solder the wires into a solid loop. Solder wont stick to stainless. Job done.

Buying a new earth lead is easier but as I said the shops were shut.