I have a 97 Mazda B-4000 SE 4.0L Xtr Cab (same as a Ranger XLT), with 98.4k miles. The original Motorcraft Alternator finally gave up the ghost, fortunately the battery still got me home. I bought a new, no doubt Wuhan CN made, Alternator (aren't they all these days) AFD0012 through Amazon distributed by DB Electical rated at 95A like the original Motorcraft, same in physical size. Their site and the chart on the Amazon lists it as compatible to my B-4000 and the equiv Ford 4.0L V6 XLT Ranger too. Installed smoothly in <45 minutes (not my first rodeo), but I immediately noticed that the voltage at the battery terminals was barely over 12.4 V. I then measured it with a DVM at the + voltage terminal on the Alternator to an engine ground at 2k RPM =2.3V and 2.5k RPM = 12.2V! When I turn on the headlights, there is a very noticeable drag on the running, but doesn't kill the motor.

Oh, I did test the Amperage output of the Alternator with my ancient Craftsman Engine Analyzer system and it showed a 10AMP output at 2k RPM.

So my question is, is it obvious the Chop Suey Alternator is bad (probably 1 or more diodes open in the rectifier), or could something else be limiting the voltage output? All the connectors are fine as far as I can tell, no corrosion, fit well to the Alt. What else ??

The original Alternator was occasionally "spiking " in voltage output, first 5 to 15 minutes of running (on initial cold start up) shooting up to a "pulsing" 14.8 to 15.2V for a couple of months before it died.
The Dash Battery warning light was intermittently flashing and then would turn off when voltage dropped below 13.8- 14.0 V. (I have a cigarette lighter port Digital Volt Meter.)

Appreciate any and all thoughts, except the crazy ones.

how old is your battery?

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Battery is a Heavy Duty, 48 months rating and is 28 months old. When I charge it with an external charger 13.5V at 2Amps for 4 to 6 hours it holds a 12.8v charge for 48 hours.

I don't see how a battery condition would inhibit (to below 12.4v) the voltage output of a new Alternator measured at the alternators B+ terminal to chassis ground.

I've also tested the 3-wire cable to the Alternator, with the ignition OFF - Yellow wire shows 12.5V, the associated 15A fuse is good, green wire is showing 0 volts(as it should) until you turn on the ignition (not start) then 12.5V, and the associated 7.5 A fuse is also good.

The "Fused Link" from the Neg Battery post to chassis gnd is also good.

If you are getting 12.5 V at the alternator with the engine running and 12.5 V at the battery, the Chinese alternator is bad.

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Turns out that the Ground lead in the 3-wire Connector was bad, fixed it and the Alternator is putting out a consistant 14.0 volts.

Problem with the "Red" Alternator is solved.