Alternator / Battery Issues
Turbo Mini Forums

So I just bought a new 70 amp alternator because I thought the old one was broken.

It wasn't charging the battery and the volt meter in the dash slowly dropped its reading over time as the battery drained. When I replaced the alt however, I was still left with the same problem...

The voltmeter now reads 12V (with a fully charged battery) give or take but doesn't rise to the 13/14 mark its supposed to when the engine is running and the ignition light doesn't turn off.

I'm totally stumped as to what has gone wrong as its literally just had an MOT and service.

The only thing I can imagine is that there is a break in the circuit somewhere?

Ideas on how to rectify the problem guys??

Test out the wiring to the solenoid from the alternator, test out between the brown/yellow wire from the alternator to the warning light, and from the other side of the warning light to white on the loom.
Sounds like a dodgy connection or broken cable somewhere.

have you tryed the light on the dash/ does it light up with the ignition on and the engine not running?
the bulb does 2 things, if it blows it doesnt charge the battery

Yes i moved to the darkside

Instagram @jdm_brett

The light will light up with just the ignition on and the engine not running, yes.

It stays on however when the engine is running or driving when it should go out.

Is that what you mean Brett?

the light is on that confirms 2 things, the bulb has not blown and it is earthing out on the alternator both should happen, with the engine running the alternator should now start charging the battery and instead of earthing the bulb it gives it 12+v and the bulb goes out,
yours does not do this bit indicating that its not charging

have you checked for broken wires ( specificaly the thick brown ones) from the alternator to the solenoid?

pull the plug off the alternator and using a voltmeter test for voltage, you should see 12v on the 2 thick brown ones all the time and 12v on the thin brown and yellow one when the ignition is on
this is sounding like an dud alternator, is it 100% new? can you get your hands on a confirmed good one to test?

Yes i moved to the darkside

Instagram @jdm_brett

I havent checked any wires specifically no, but the harness/loom is all fully taped up and doesn't look frayed anywhere. There could be a break somewhere though...

I'll have to check the alternators output next weekend as I don't get home til late weekdays.

Brett, the coloured wires you're referring to, surely they won't have any voltage if the plug is disconnected from the alt?

Or are you referring to testing the spades those respective wires connect to?

Yes, the alternator is brand new, and it was the same case with the old alternator before I changed it over...so unless i've had bad luck with two alternators being dud, i'm starting to think he wiring has gone up the shitter somewhere along the line

If you pull the plug off the alternator, you will still have voltage without the engine running, as its bolted directly to the battery cable terminal.

Ah! Gotcha

The battery warning indicator on the dash ( the red light with a battery on it ) will only illuminate if there is a ground. If the wire is broken, or it is not attached the alternator, it will not illuminate.

If what you are saying is that the battery warning light is illuminated with the engine running, and the brown/yellow wire is attached to the alternator in the correct manor, the alternator is goosed