Any way to test Boyer Power Box?

Hi all,
73 850 fitted with Power Box to convert the alternator AC to DC to charge the battery.
Has been working just fine for the 12 years!

Now, battery not charging. New battery.

All wiring and connections look very good.

Can anyone suggest some tests to be done with my digital voltmeter at the alternator wires connecting to the power box?

Or, a simple way to verify that AC current is even coming out of the alt wires prior to power box?

Or, could my power box have suddenly croaked and how to know if I need to buy a new one?
Thanks for any comments

If you get proper AC out of alternator wires (engine running ) the fault is probably in the box. Disconnect the black and red wire at the box and take a DC reading. If AC goes into the box and no DC out - box is crap.

Connect a headlight bulb, [a car sealed beam or bike bulb around 50 or 60 watts] to the two wires from the stator. Disconnect them from the power box first. The bulb should be brightly lit by about 3500 RPM. This is a simple go - no go test.

If you have output from the stator and you have no charge then the power box is bad [rare] or you have connection problems somewhere between the box and the battery.

You need a 1 OHM 100 watt resistor. The altternator wires hook up to it. Now known base lines can be checked out. looks like this and Steadfast had some on evilbay just of late.

To wire for test, see Lucus manual. This also has bench marks.
For low buget quick down and dirty a 12 Volt,light bulb rev and blow test again right off the alt. wires.

Excellent! Thanks for the replies all.

So, you are saying that I can take out my headlight bulb and while the motor is running touch the two wires directly from the alternator to it.

One wire presumably to the center and one elsewhere on another part of the metal back of the bulb?

And if the bulb lights up, my alternator is working.

I am confused about another suggested test: If I remove the red ground wire from the boyer power box, and also remove the black wire going to the negative battery terminal, it was
suggested that I connect my volt meter, but to what do I connect it to? The now disconnected black and red wires perhaps? And with the motor running this will tell me what?

Thanks for your patience with me on this!

One wire presumably to the center and one elsewhere on another part of the metal back of the bulb?

>>that would work<< Might want to be careful. If the alternator is working and you are touching both wires at the same time you can get a bit of a tingle.

And if you have power there then you can use the bulb on the black and red wires that come out of the power box and see if you have power making it through the box.

NOW I got it!

Thanks for clearing that up for me, Jim.

Well you had all ready done the most common test and it failed. That is bike running voltage tester on battery terminals than rev motor 3500RPM = see volts go up to 14 or so and stop. All this with a charged battery that has been load tested.(so you know your base line volts at battery)
So yes low beam filament to alt. wire and bulb case to ground. But now that the wires are bare you could also do other testing with the volt meter. Meter set on continuity all the wires out of the alt should have no continuity to ground. AMP gage test even better the bike needs APM's to run and charge. This real life test has you interupting one of the battery wires with an AMP gage. Now the easy to read AMP's can be checked under real load, bike runing lights on to see if there is an AMP left for the battery charge. Much better test AMP meters are cheap so is the Lucus book. page 34