It's the same with Datsun alternators. The "field" of the alternator is connected to the dash light. If the light is burned out, it won't charge.

Late on they added a resistor in parallel with the dash bulb, so even if the light burns out it will still initiate charging.

I had a recent alternator charging problem: it was charging because of residual magnetism in the core, but suddenly stopped charging when the core degaussed sufficiently. It turns out that on at least some cars (possibly not datsuns) the alternator charge light on the dash actually controls the field voltage on the alternator, and if the light's not connected (or burnt out) the alternator will work for a while, but possibly not indefinitely.

Good on ya

I've got it Sussed, went through tech wiki, bypassed the reg and the rest was a guessing game, alt light on the dash isn't working but the alt is charging and the car is not on fire so it's happy days.

What alternator did you have before the 4A was working?
Is your 4A alternator the kind shown in the photo above (with IG/L round connector)?

Voltage Regulator looks like one of these (short or tall, various colors)



With late utes (straight battery placement) the Voltage Regulator was typically placed on right side (next to battery).

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  regulator_late.jpg (97.35 KB)

The A series engine was removed years ago so I have no idea what it looks like, excuse ,y ignorance but what does an external regulator look like and where would I find it?

Appreciated the help

For 1985, in some markets it was still externally regulated. Dunno about your country. If you look on the back of the 1200 alternator, markings of FN mean externally regulated, while markings of SL mean internal. Who knows if your 1985 ute even has the original non-modified wiring. So best to look.

The CHG wire does not normally go to the alternator unless it has been converted to internally regulated. Which kind did you have until now?

So an 85 A12 Alternator is not internally regulated?

I can see a thin white/black wire there, could that be the chg wire?

Oh, almost forgot.

Once you disconnect the old external voltage regulator and throw it away, the two wires (in the original 1200 wiring loom) that go to the alternator will not have any connection. Because they are normally connected inside the voltage regulator.

So run two new wires to the new alternator.