I made the mistake of telling my wife that there was absolutely nothing wrong with my 240. Within 20 minutes the voltmeter dropped to 11 volts and the headlights started to get dim. The weird thing is that the amp light did not come on. So far this is what I have done:

I have checked the exciter/warning light circuit. The amp light will come on if I ground the exciter wire.

I measured 12 volts on the big red wire post on the alternator (battery connection good)

The alternator case has continuity with the engine and the ground wire is in good condition.

The belts are tight.

I have tried another brushbox/regulator (not new but was working when removed).

I have put on another alternator (not new but working as far as I know).

After all this I still have the same symptoms. No amp light with the engine running or off. No charge. I am stumped. I suppose the next step is to get the alternors tested. I just can't believe both alternators would have exactly the same symptoms. Have I missed something?