So I do I test this thing Click to view attachment

Test it in another 914. Don't you have more than one?

Throw it in a lake. If it floats, it passes. Then get a new one, and wonder what else is wrong.

..I have a few in my stash....just want to know if I should throw it away...

No.... just one now.

2 ways to test it.

Put it in the car; start the engine and see if it regulates the battery voltage to about 13.5 to 14V. Must measure at the battery. This assumes the alternator and all wiring are ok.

Test it on the bench. A bit more involved. Put a DC voltage across D+ to D-. Put a load resistor of some value equal to the resistance of the alternator armature; maybe 100 ohms between DF and D-. Vary the dc voltage from 12 to 15V while monitoring DF to D-. Below 13.5V (D+ to D-) the voltage from DF to D- should be near the DC input voltage. Above 14V (D+ to D-), DF should be zero volts. I've never tested one like this but this method should work.

Thanks Jerry I guess I'll just put it back and do the test.

With a tester, how else....?

These are basically a relay with an op-amp comparator to control the position.

Above ~14 volts, the relay should open (take the alternator input away from the battery)
Below ~13 volts, the relay should close (putting the alt output back onto the battery).
The deadband (should not change state) is between 13-14.
So if you had a variable voltage power supply, you could check the transition points.

I know the older units in the type-I engines were physical relays and you could hear them buzzing when they were working but hard to hear over the engine noise and are not doing anything unless running.
The newer ones you can buy now (solid state) have no moving parts so make no noise.

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