The small alternator terminal is sort of a ground but not a ground.  The small alternator terminal is to the stator windings.  When the key is in the run position (engine off) current flows from the ignition switch, through the warning lamp, to the alternator's small terminal, through the stator windings, and on to ground.  The flowing current lights the warning lamp.  This also energizes the alternator coils so current will be generated as soon as the alternator starts spinning.  Once the alternator starts making electricity, it raises the voltage on the small terminal to full system voltage (nominally... 14V to 14.5V).  When that happens there is no voltage difference across the warning lamp so it turns off.

If the lamp works when you ground the small brown/yellow wire, that says the lamp, wire, and ignition switch are OK.  With the lamp known to be good, if it does not light when connected to the alternator the problem is in the alternator or with the alternator's ground connection.

Thanks Doug   I have already done pretty much what you have suggested and to no avail.     The small wire to the back of the alt is the ground wire to the warning light (brown/yellow).    The terminal on the back of the alternator that this attaches to is not grounded with/without the engine running, therefore the light doesn't work.  I'm thinking either there's a problem internally in the alt. or this particular alternator will not make the warning light system function on my mini.  I guess what is bugging me the most is this was sold as simple conversion and it was (except for the belt) but it doesn't work.

In general, when you describe an alternator as "2 wire" it implies that one is a large terminal/wire that delivers the output current while the othe terminal/wire is small and is used to supply the stator windings to energize them on initial start.

I suggest a quick test.  Make a tester from a turn signal lamp with two wires solderd to it OR use one of those awl type circuit testors.  Connect the wire from the testor to the solenoid terminal with all the brown wires (permanently hot).  Touch the point of the tester to the small terminal in the alternator (if using a two wire test lamp, connect the second wire from the test lamp to the small alternator terminal).  The lamp in the tester should light.  If it does not, the issue is internal to the alternator or its earth connection.  If the test lamp does light the problem is with the small wiring to the alternator.

I know you said you used the conversion scheme on our host's web site.  To paraphrase that here, you connect ALL the small wires that were on the old control box EXCEPT the black earth wire which is taped off and not used.  You join all the BIG wires that used to be on the control box.  You either connect the old, large generator wire to the olternator or you run a new large output wire from the alternator to the solenoid terminal with all the brown wires.  You connect the old, small, brown/yellow wire from the generator to the small terminal on the altenator.  That's all there is.

To test the charge warning lamp, disconnect that small brown/yellow wire from the alternator and with the ignition on, earth that wire to the engine block using a jumper wire.  If the lamp does not light, replace the lamp and try again.  If it still doesn't light, look for issues with the wiring to/from the lamp and look at the ignition switch.

Curious what alternator did you use? I did this to a few classic hotrods and I'd like to find out how you bypassed the stabilizer. Also a photo might be nice for reference. I dunno what color of wires your attaching to what...

hec

I just installed a compact alternator on my 1965 Cooper S  it is a two wire alternator the same as the two wire generator I removed.  I have rewired the Lucas voltage regulator as per the instruction on Mini Mania's web site (I DID NOT GET THE ALT FROM MM ) my problem is the ign./alt failure light  no longer is illuminated with the key on and the engine not running.   Any thoughts are previous experience with a fix for this would be appreciated.    Thanks  Jim