Alternator gone or could it be a problem with electronics?

Set out on a trip on Friday night - about 30 minutes out suddenly all the dashboard lights come on (not the oil pressure which is on a different circuit) and the alarm buzzer starts up. I think I have worked out that if the alternator is not charging this is what happens, is that right? The engine seemed to be running fine. And can anyone advise where I should start? It's a 1991 Hiace with 3L series diesel engine and automatic gearbox.

The question is, alternator gone - or could it be the ECU or other electronics/wiring faults? Incidentally after waiting 3 hours for the breakdown service I decided to drive home assuming the batteries would have enough juice to get me back (which they did). This time the lights and the buzzer went off and I could see that the battery was charging for a while - then after about 8 or 9 minutes the lights and buzzer came back on and charging stopped. Anyway I got home safely

If it's the alternator, should I replace with a new one, a reconditioned one, or try to get mine repaired? Any advice welcome. It's a bit of a drag as I have just replaced the cylinder head.

One last question, any way to switch the alarm buzzer off - It's really loud. It would be great to have a switch so that if it does come on I wouldn't have to drive home with a deafening noise ringing in my ears.

This can also be caused by the water detector at the base of the fuel filter IIRC, so get someone to drain a bit off (There may be a sort of tap right at the bottom) or to refit or fit a new fuel filter if it's old.

Wear gloves as diesel is smelly!

I don't think the alternator not working makes the buzzer buzz. There are two buzzers, one behind the speedo and one behind the dash on the RHS.

Your headlamps will show you if it's charging BTW, if you start up the engine and they get brighter the alternator is OK. You can also get a voltmeter to plug into the cigarette lighter socket:
https://www.ebay.co.uk/itm/USB-3-1A-Car-Cigarette-Phone-Charger-Lighter-Digital-LED-Voltmeter-Accessories/254338356319
And see if it goes up (14V or so - they are not super accurate) when running.

If it does turn out to be the alternator it's probably just worn brushes so first check would be those before spending out on 'reconditioning' or replacement, otherwise it could be the regulator. A voltmeter will soon show as @GPW says. Worn brushes can make intermittent contact when they're right at the end of their springs so may work occasionally for a short time.

Thank GPW and AgathaAlice. I do have a crude voltmeter plugged into the cigarette lighter socket - just 4 volts - but that was showing that it was not charging while I was having this problem.

Presumably replacing the brushes means getting the alternator out? Are replacement brushes easily available?

I have the same engine as you (3L). I bought a set of brushes just in case off of eBay, here is a link to the auction. Part No. 27370-75060

Here's a link to the part on JP-CarParts.

It seems like you might be able to get the brushes out from the backside of the alternator without removing it, though I haven't needed to try, thankfully!

If your reading was actually 4 volts you've got more than an alternator problem! However I'd suspect something wrong with the meter or its connections. With no charging you should be seeing something around 12 volts minimum and with charging as stated above somewhere around 14 volts, maybe as high as 14.5 volts. Remember that many vehicles switch off the cig lighter through the key so if you didn't have the key on and got 4 volts it may have just been charge stored in capacitors in any accessories; check again with the key on but the engine not running.
I'm not sure if the brushes can be accessed without removing the alternator, it would be really good if it was possible specially if your alt. is like ours with the vacuum pump for the brakes attached and oil lines for lubricating the pump bearings which makes it a PITA to remove and refit.

Sorry not 4 volts - the plug in has just 4 lights on it - when it's charging all 4 light up but when it's not just two lights. I've ordered the one suggested

Hi Andonic
You might have fixed it by now. But some time back the alternator failed on ours while my daughter has it and she drove it till it would not start. Had to have it towed to my place.
It had some lights on too. I think the alternator light was on and some other orange lights. These are just a warning to do something and will go out when you fix it. The alternator had failed but it was probably fixable earlier but was burnt out by this time. That is my experience of these ND alternators if you do not fix them early. It was not just brushes this time either and the regulator was bad too.
I ordered a new alternator and fitted it. Not the easiest job but doable if you are handy. Here is a site which i use to get the original part numbers for Japanese import parts. When you have the original number the suppliers can usually supply a direct replacement. It will be accurate if you use the numbers on the Toyota information plate.
https://www.megazip.net/zapchasti-dlya-avtomobilej
Good luck
Jaahn

Took it to the garage and they confirmed the alternator had gone. Replaced it with a Lucas one - £168 (and VAT and Labour). Pleased to have it fixed now and hope to have no more big bills for a while - but the old girl is 28 years old so I suppose things will go wrong from time to time. Thanks guys for all the info.

Hi my alternator went and got it fixed locally for £75 took a week and was dead easy to remove and refit