I have a 96 ford ranger 4.0. Saturday morning I noticed the battery light flashing off and on so I decided to pop in O'Reilly s and get it checked. Of course, alternators bad( voltage regulator fault). Changed it drove home light still on. Decided to go back get it checked. Voltage regulator fault again. OK. Put in another alternator. Watch the bench test. Checked fine. Drove for awhile did OK, no change in battery volts but light went off. Turned on headlights and boom started draining again. Got checked voltage regulator fault again. I've checked connections checked fuses replaced and redone even though they seemed fine. Please someone help I'm losing pay today and don't even know where to begin.

 

Not to sound sarcastic but have you actually changed the voltage regulator...

 

You're fine and it is internal voltage regulator also I did test green wire has no power when key is turned on

 

Green wire is the ON/OFF switch for alternator and should show battery voltage with key on, its also the Battery Light circuit, so surprised the Battery Light is on????

Check Fuse #15, 15amp in 1996 cab fuse box, that powers battery Light circuit/green wire

Battery 12v-----Ignition switch-----fuse 15------------battery light bulb------(green wire)---------voltage regulator

The 12volts passes thru the battery light bulb to the voltage regulator, when alternator is not spinning it is 0 volts, so a Ground, battery light bulb lights up, once "working" alternator starts to spin it generates 13+ volts, so not a ground and fuse 15 is also 13+volts now so BOTH wires at the battery light bulb are equal voltage, so bulb is off

A Battery is only used to start the engine, it is not used again until you shut engine off and restart it.
Battery runs 12.3 to 12.8 volts, vehicle/alternator runs 13.5 to 14.5 volts when alternator is working, so no power at all comes from battery at that time

When battery light comes on, or flickers, it means Alternator Voltage is below Battery Voltage 12.5v, and Battery power is running the vehicle, a light bulb can only light up when it has two different voltages, like when key is on but engine is off

 

So I put another alternator in. Its brand new. Still same problem. What am I missing. Is there something that would cause voltage regulator to not work.

 

Yes, no 12v on Green wire with key on

Also no 12v on yellow wire, it should have 12v key off or key on, Fuse #17 in engine fuse box, 15amp

B+ is the terminal on the back of the alternator, the stud and nut terminal, that terminal/wire should also have 12v key off or on, it uses a Fusible Link on that Black/orange stripe wire in 1996.
So no 12v there means Fusible link has blown.

And that all there is to testing alternator wiring.
Green wire, 12v key on only
Yellow wire, 12v all the time
B+ wire, 12v all the time

There is a white jumper wire on some models, make sure wire is not frayed and that it is plugged into alternators spade connector