Are there any other lights on in the dash? Any chance the dim alternator light is really light bleeding over from another bulb?

Always on... as in never stops glowing when the key is off? That would indicate power is applied to an ignition sourced circuit. Maybe an added circuit is looking for ground and is finding it through the ignition wire to the dash light?

Always on... as in glows when the engine is running? That indicates a path to ground exists for the battery light after the dash.

If it glows when the engine is running, does it generally stay at constant intensity? IOW, if dim, does it tend to stay dim? If bright, does it tend to stay bright? If fairly constant, it may indicate the path to ground is through a component that has been inadvertently connected to the battery light ground wire from the regulator. If you've tied into any wires that are powered at key on, you may want to confirm the vehicle wires are not blue or white/blue before troubleshooting the alternator further. You might also have a short somewhere in the signal wire or a problem with the stator. Disconnecting the wire from the alternator will quickly tell you if the problem is internal or elsewhere in the circuit. With the wire disconnected there should be no path to ground and therefore, no light.

If the light glows with varying intensity and appears to brighten with increasing engine rpm there's a good possibility its related to the alternator.

I had trouble with brush misalignment on a Bosch alternator on my personal vehicle. Part of the brush overhung the edge of the slip ring and eventually made contact with the rotor. That one illuminated the light dimly at low rpm. Once the regulator was removed you could see the brushes were not worn evenly. It's a long shot but something I happened to remember. I couldn't get the regulator to align so every 3-4 months I would remove it, grind down the high spot, and re-install.

Sometimes when the light is dim and intensity varies with rpm it's because the rectifier in the alternator is allowing some A/C current to bleed through. It's caused by a faulty diode. You'll see proper charge voltage with a voltmeter and everything will seem to work, but with an oscilloscope there will be an obvious ac rider on the dc trace at the BAT wire.

A battery drain would cause the alternator to charge at a higher rate for a longer time than normal once the vehicle is restarted. This should only cause the light to illuminate if the alternator has been forced to recharge a very low battery frequently enough that heat has ruined the alternator. In this case the light is illuminated by a faulty alternator however, the cause of the alternator fault is external and needs to be corrected. If the supplier is reasonable then he's checking to ensure that a replacement alternator won't fail due to conditions out of his control. However, imo, if the car has been cranking fine and has not needed to be jump started, then the battery is not being drained enough to ruin the alternator and the "draw" test should be just a formality. On a similar note, add-on accessories that draw large amounts of current will force the alternator to operate at or near full capacity and ultimately the heat this generates can ruin the alternator. Do you have an idea how many amps you're using with the components in your conversion? Do you have any high current accessories added? Regardless, if high current output has killed the alternator the immediate problem is still the alternator. A decent local garage should be able to test your alternator on the car. They'll charge a fee, of course, but maybe you can get the alternator supplier to agree to cover it if the alternator proves faulty. Some of the chain stores have alternator test stations as well. If you bring in the alternator they'll test it for free. Ask if you can watch the test so you can see the results. Or you might have a local rebuilder that has equipment to perform a full evaluation on the alternator. They may be willing to test the alternator for free as well. Of course they'll try to sell you a gazillion amp, nuclear bomb proof, EMP resistant replacement if yours is bad but sometimes it's worth it to listen to the sales pitch.

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