T25 1.6TD Alternator not charging battery

[uladk84]

Hello all!

I have an urgent problem as my alternator is not charging my battery. It is urgent because I'm stranded abroad in Italy. A nice place to be, but I can't stay in this campsite forever!

The situation:

- van has been running for 2 months straight, no issues
- when bought it had electrical issues, (some cut wires, random wiring, a lot were fixed)
- battery indicator light on dash has never worked
- alternator voltage is the same as the batteries
- I was at the campsite for 3 days (no engine running), and I removed the battery to get to something else. I suspect a broken wire, as everything was working before moving the wiring. (I rewired everything correctly).

I have read many posts but need confirmation as I'm a bit confused. My alternator, has 3 wires coming out of it:
- large guage red (attached via bolt) going to battery pos
- small black/red (attached via bolt) going into a connector next to the alt
- small blue (attached to spade) that is cut

Questions:

Is the blue wire the for the dash indicator bulb?
Is the exciter wire red/black wire?
Where should the exciter wire plug into the back of the alternator?
Should the exciter wire measure 12V with the engine in he 'ON' position?
Will grounding the exciter wire turn the dash bulb on? (to test for harness integrity)
What route does the exciter wire take to front fuse panel?
If the exciter wire is supposed to measure 12V, where can I test it up by the front fuse box to see if I have a broken wire further up?
How can I test the dash battery indicator light from the front of the van?

Any help would be incredibly grateful or our 1986 1.6TD, or 'Dotty' as she is known!

Thanks!
Lewis

[Oldiebut goodie]

Blue is usually the exciter wire which also shows as the light on the dash, without this connected you will have trouble charging the batteries. Should read 12v+ with ignition on, 0v when alternator running.(Alternator output negates the 12v from the dash)

[ianboydsnr]

Borrow a charger, charge up battery,

Start van and drive it back during daylight, stop somewhere where there is electric and charge battery again,

Diesels don't use much electric once running, especially if not using lights,

Get home then sort out!

[uladk84]

Cheers guys,

I reconnected the blue wire coming out the back of the alternator, and tested the voltage at it, which was the battery voltage. Only problem is that the wire reads battery voltage while ignition is both ON and OFF. As I understand, it should be be 0V in the OFF state, 12V when ON, then 0V when running. The battery dash light also never turns on with the ignition ON, but if I put the blue alternator wire to ground, the dash light it on.

Any thoughts on how this could happen? Worn ignition?

I noticed that my blue alt wire is two different blues: a baby blue from the alt, then joins to a darker blue (previous owner made the cut), that runs into a connector near the alt. A red/black wire runs with the blue wire from the alternator to the same connector. The connector wires then trace back to the black box in the engine bay.

Thanks

[Oldiebut goodie]

The blue wire should only be at 12v with ignition lights on - the 12v+ comes from the dash, through the bulb and then earths through the non running alternator lighting up the bulb. Someone must have carved up the electrics so it is hard to know what to suggest. Except to remove that black/red from the connector - it is most probably that feeding the voltage to the blue wire, which isn't what you want.
Then test the output voltage.
What is the alternator voltage? If you are seeing voltages above 14v or close to that your alternator is charging.

[uladk84]

Thanks.

I disconnected the ignition connector, and all the red wires going to battery pos except the one coming from the alternator. That still gave me 12V at the alt blue wire. If I then disconnect that heavy gauge red alt wire from the battery, the voltage is gone. The alt red and blue wires are wrapped in the same protecting tubing so I'm betting if I open that up, I'll find they've rubbed together enough to wear away the insulation, and the red is providing power to the blue exciter wire.

I'll find out tomorrow, it's late!

[uladk84]

Well... now I only have the alternator connected via the red wire to the battery, nothing else, yet still see 12V at the D+ terminal (with the blue wire removed).

Something broken inside the alternator?

[ghost123uk]

Except to remove that black/red from the connector.

I am thinking that the previous owner might have added that black/red wire to the blue wire to trigger a split charge relay. If that relays wiring (usually near the battery) has been disturbed maybe that is why there is 12V on the blue wire all the time ?

[ghost123uk]

Well... now I only have the alternator connected via the red wire to the battery, nothing else, yet still see 12V at the D+ terminal (with the blue wire removed).

Is this 12 Volts you see with the motor running ?

If yes, try temporarily connecting the blue wire, from the alternator to the main (heavy) output terminal on the alternator and then fire it up. Measure the voltage. If over 13.6 Volts your alternator is basically OK and you could get home, but take the blue wire off when you park up. Before doing this though, wait for "Oldiebut goodie" to confirm that my idea is sound

[uladk84]

The 12V I see at the blue alternator terminal is with the motor off, ignition and everything disconnected EXCEPT the red wire from battery to alternator. This is the only wire connected to the battery.

I have seen the 12V at the blue wire with the ignition running too, but disconnected everything to isolate the problem.

Looks like it's an internal short in the alternator. Any advice aside from getting a new one?

[ghost123uk]

OK, so you have 12 volts on the blue wire. You connect it to where it is supposed to go on the alternator. You measure the output of the alternator on it's main terminal and you still only get 12 Volts. If that is correct then, yes summat is wrong with the alternator. It might be just the brush pack = common failure and only around £15 plus 5 minutes to fit. Or, the alternator itself might be duff. Many VW cars of the similar era use the same alternator so a replacement shouldn't be too hard to get. They even have breakers yards abroad I guess. The only thing you might have to do, if buying another alternator, is swap the pulleys over, and that can involve a big hammer, lots of heat (from a blow torch) and some swearing.

p.s. = Do I seem to remember from doing mine, (broke down in York) the nut holding the pulley, is it a left hand thread ? (useful to be forewarned if it is )
E D I T = I just did a bit of Google research and from what I can see it is not left hand thread, but I stand by to be corrected

[Oldiebut goodie]

I am not sure whether the voltage has been tested with the engine and alternator running yet and the blue wire attached. That is what we need to know to be sure of anything.

(I'd like to see someone drive back from Italy at this time of year with no heating blower, lights etc! )

[ghost123uk]

OBG, I know you know about exciting alternators If one was to directly connect a short (blue) wire from it's terminal on the alternator, to the main output terminal on the alternator (with it's 12 volts from the battery on it) would that work to excite the alternator, or do you think it has to have a bulb (or similar resistance) inline to prevent too much current flowing?

I mentioned this idea above, as a temporary test, but not sure if it is sound.

[Oldiebut goodie]

As far as I have been able to ascertain it is a minimal amount of current that is needed so any ignition switched live would suffice if the wiring is mullered at the dash end (Not unusual!) (when I have resurrected generators with excitation it takes next to nothing to get them producing the ac)
Your method will work - the battery is very close and you could take it from there also rather than fiddle around the back of the alternator. A very rough and ready method is to use two long wires to do this and make the connection under the rear seat (switch or even just twisting wires together, insulating each bare end and the joint each time) This would save getting in the engine bay under all the travelling gear at every stop!
A method that I have just thought about but not tested - connect the the blue wire to the glow plugs busbar and the excitation takes place as the glow plugs are used and the engine started then switches off when they do. The alternator should remain excited without any further need for excitement. Just means that if the glow plugs aren't needed, unlikely at this time of year, it wouldn't work.

[ghost123uk]

That glow plug buss bar idea is good lateral thinking

I was concerned about how much current would flow into the alternator exciter terminal (at rest) with no resistance (bulb) in the circuit.

Of course, ideally the OP should sort out the fault in the circuit to and from the ign lamp (but maybe best done when back home )