Alternator issue/argument!!

[Oscar the Grouch]

Hello!!
We are the proud new owners of a 1983 VW T25!! Awesome, except we have got no further than the end of the road and had to be towed home!!
I have followed a few conversations on club 80-90 and have learnt a lot (we are complete novices!)
I really hope one of you can help??
The battery had a drain (brand new battery) which we found to be the alternator, today we removed the alternator but on doing so we found the wire to the dash warning light was disconnected!
Before we completely removed it we tested the battery with a multi meter whilst we connected the wire to the dash, but still no charge.
Only after the alternator was out did we remember that we had already removed the regulator! Doh!!!!
So my predicament now is should we reinstall the original Bosch alternator (with the regulator and the dash wire connected) just in case it might work or just suck it up and install a new (non Bosch) alternator?!?!?
Our family member mechanic is adament that it won't work because it got hot, I really don't want to annoy him by asking if we can just try the old one again just for my piece of mind, but its really niggling me!!!!
Hope I haven't waffled too much!!
Looking forward to your opinions!!
Kind regards

[itchyfeet]

You can usually find a local company who will rebuild your alternator for a fraction of the price of a new one.
No point messing around I had mine done for 50 quid but it took a week.

the charge light wire is needed or it won't charge the batt.

where are you, what engine/van?, stick it in your signature helps us to help you.

oh and welcome

[Oldiebut goodie]

Usually if an alternator is draining the battery it means that one or more of the internal diodes has failed, whilst repairable by some of us on here it is more likely that you should leave it to someone with the tools and know-how. I second having it repaired if you have a local refurbisher. It is unlikely that it would work even with being connected up correctly if you/mechanic is certain that it was causing the battery drain.

[Oscar the Grouch]

Thank you so much for your fast and very helpful responses!!
I can see I may be spending a lot of time picking brains on here!!
Hopefully once we've sorted the alternator we will finally be on the move!!
Oscar is currently referred to as the expensive picnic table!! Ha ha!! Our boys love to have picnics in it even though it's just sat on the drive!! Makes people smile when they drive past!!
Again many thanks!!!

[ghost123uk]

I'm not that familiar with the air cooled variants, but I do know that the alternators fitted to many German vehicles of similar age are the same as the alternators fitted to the water cooled T25s (and very likely air cooled as well), possibly just needing a pulley swap (or not), so a trip to a breakers should result in success. Take your old one with you to compare Just another option.

[Oscar the Grouch]

Hi!! Still having issues with our alternator!!!!!
We are currently trying the old alternator again but we have found that the battery light on the dash is illuminating without the key in the ignition!!?!?!?!?
Any ideas would be most welcome!!!
Thanks in advance!

[Oldiebut goodie]

If a diode has failed it may be feasible that the battery is feeding back through the alternator to illuminate the light. This is most probably why someone disconnected the wire originally instead of sorting the problem.
Ghost - have you any thoughts on this happening?

[Bubble Meister]

The power supply for the dash (battery light, oil light, indicator light, temp and fuel gauges) all should come directly off a black wire direct from the ignition switch and this wire is only powered when the ignition key is turned ti the run position. The wire goes into the dash multi plug at pin 8.
You say the battery light is staying on with out the key in - are the gauges powered up and the oil light? If not then it may be that someone has tinkered with the power supply to the battery warning light. If all of them are on then the power supply is wrong - it should be via the ignitio switch with the key turned to run.

Around the battery warning light tthere's a resistor (to prevent the led light from blowing) and a diode ( this ensures flow is from the ignition switch to the alternator and not the other way around).
After the warning light the signal goes to the alternator (leaving the dash multi plug at pin 11) via a blue cable.
Remove the plug from the alternator and check if the battery warning light is still on? If so, there is an incorrect path to earth somewhere.
With the alternator plug removed ground the blue wire and the battery warning light should come on, if it doesn't there's a power supply problem.

UUsing the above in conjunction with the Haynes manual or other vw wiring diagram should make sense. Let us know the results.

[Oscar the Grouch]

Thank you Bubble Meister and oldie but goodie!!!
We tried earthing the blue wire but the bulb did not illuminate.
The bulb illuminates without the key in, but goes off when the ignition is on!?!?
I'm ageing quite quickly!

[Oldiebut goodie]

It will be a bulb especially on that age van, the output from the alternator rises in the blue exciter wire until it is equal to the voltage being fed to the alternator from the main power supply, at equality there is no voltage difference therefore the bulb light is extinguished.
The battery light's behaviour as above points far more to diode fault than dashboard wiring issues, especially as the bulb is receiving power from the alternator with no key in but the voltage levels are equalled with the key in and the light is extinguished. (there is power to the alternator at all times when the battery is connected but doesn't flow due to the diodes normally)

[Bubble Meister]

Replacement diode pack for the alternator (if not soldered in)?

[Oldiebut goodie]

I doubt that the OP would be able to do it as stated earlier, I use a 150W iron but sometimes needs more. (Usually soldered in)

[ghost123uk]

Still reckon a tenner spent at the local breakers is worth it, though the charging light issue is a bit weird. OK, if the diode pack (note to Oscar, that is not the same as the brush/regulator pack) is fubarred then yes, 12V could be feeding back to the lamp, but when the ignition is off it should have nowhere to go (open circuit), so the light should be off.

I reckon a methodical go over with a meter is called for.

Tests with ignition OFF:-
Is there 12V present to the bulb from the dash end of things (with the blue wire to the alternator disconnected)? - If yes, a dash end wiring issue.
Is there 12V present on the terminal on the alternator the blue wire goes to (again, with blue wire disconnected)? - If yes, a duff alternator.

[CovKid]

Agree on breakers. I did that 10 years ago and the secondhand 90amp still going strong.

Just took a few minutes to swap pulley, plus I think, modding the plug connector but wasn't hard. Your alternator definately won't be unique to your engine and new/refurbed ones are daft money.

[Bubble Meister]

Can the OP clarify these points:
1. With the key out the bulb is on so how do you stop this from draining the battery.
2. You said the bulb goes out when the key is in the ignition switch
a. I assume this is with the alternator fitted?
b. Can you clarify whether the engine is running or not when the bulb goes out?