Ignition light on.

[Chris]

If it is a Delco alternator with the nine diode system then it will be the warning light diodes that will need
replacing so as to give you an indication to what is happening in the charging system .
As you mention the alternator is charging correctly at 14 V, if the stator windings or any of the other diodes
in the six main diodes were faulty you would have reduced charging that would be indicated by a slightly
glowing warning light, if the warning light diodes are working correctly .
Hope that makes some sense, you should still be able to buy these warning light diodes but if you can't,
contact me and I can help you out .
Chris.

[aaronjb]

1-wire alternators don't (easily) support a battery light.. I think there are modules out there you can buy to mimic the standard behaviour, but as it is you might as well just disconnect your light, it's doing nothing

Long version:
A 3-wire alternator or externally regulated alternator needs a 12v feed from the battery initially to 'excite' (no blue pills here!) the field coils; before starting the engine the excite line is a path to ground from the battery - and your lamp lights up. Once the alternator starts spinning and you've excited it enough, the alternator starts putting 12v *back out* on the same wire - it's no longer a path to ground and thanks to the magic of electricity there is zero potential difference across the bulb so it goes out.

A 1-wire alternator just has one connection straight to the battery (and nowhere else), everything else is done internally.


I think the modules you can get take a switched live (from the ignition switch) and 'battery' (which will read alternator output voltage when running) and turn the bulb on when battery < 13V and off when the battery voltage is >13V.. that's a simple voltage comparator circuit in reality but easier just to buy a module from somewhere.

[Dek]

So the ignition light is constantly on but the alternator is charging the battery . Battery voltage engine off 12.6v engine running 14.8v. Ford 302 single wire alternator. Voltage on red cable to lamp engine off 12.6v running 14.8v. Other cable to lamp (blue) goes to earth both with engine off and on. Explains why ignition light is constantly on. Question:is there anything else I can do or as I suspect take the alternator off to be tested for a low voltage return. Must admit I don't really understand how single cable alternators work. Any help appreciated.
Dek.