How do I wire an alternator


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Help! Can anyone tell me how to wire an alternator?

I converted back to a dynamo 2 years ago, and I need more power for the winter, I’m forever watching the ammeter when the lights are on - the charging system just isn’t man enough with electronic ignition and a decent headlight bulb.

I have a 30 Amp alternator from a Case tractor and a regulator that I fitted many moons ago and gave good service, I only went back to dynamo because it didn’t look right.

Now try as I may I can’t remember with any certainty where the wires go, and there’s only 2 on the alternator and 3 on the regulator!!!!!

The alternator has “+” and “Ex”

The regulator has “D+” “D-“ and “DF”

I’m guessing alternator body earthed (-ve) and “+” goes to battery via ammeter.

Now something tells me the “Ex” is for excitation to make the alternator charge and needs a feed from the regulator …”DF” perchance ?? And I think D+ and D- are connected to the battery to read the voltage and switch DF on and off as necessary.

Please be kind with your answers, I’m not as young as I used to be. I knew how to do it once, and the really sad thing is, I drew a wiring diagram, but I don’t know where I put it!!


ps Where does the ignition light attach?

Comet Rider

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Hi Howard,
If its similar to the "Walkernator" then yes the Ex is the field excitation terminal, which will connect to your Df on the regulator.
The D+ on the regulator should be connected to a switched live, otherwise you could end up with a flat battery.


Pete Appleton

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You are nearly right. D+ will need to be switched to avoid draining the battery when you are not running. If you have coil ignition then it can just be run off of your ignition switch.

Unfortunately, with this type of alternator, there is no provision for a charging light. You could use one of the voltage sensitive types such as the 'charge warning light' or 'battery status monitor' as supplied by Paul Goff

Sorry, Neil got there while I was typing. Lucky that we both gave the same advice.


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Thanks both. I would have switched it, I oversimplified my post.

Nice to know my reasoning still works even when my ................ errr ............... whatsitcalled.............. oh yes ............. memory lets me down.