Well my 2000 ranger 5.0 swap is having an intermittent issue where the alternator does not charge the battery. I have charged the battery voltage is at 13.5, new alternator, new mega fuse, checked all the fuses and all are good, battery light on dash works. When driving the gauge cluster shows randomly that the voltage is low, but no battery light, if I increase rpms at a red light the gauge goes back up to normal charge level. I verified I have 13.5 volts a b+ terminal at alternator, and large yellow wire. with ignition on the green wire has the same 13.5V. I am confused as to what would cause my alternator to randomly not charge the battery. Also checked all connections to battery, grounds and the connections at the starter and everything is clean, tight and nothing broken. Any other items I should check that I have not listed above and any help is greatly appreciated. Oh also this all started after the engine overheated.

 

You have a bad battery or volt meter, if battery shows over 13volts with key off

Car batteries when new are 12.8-13.0 volts
12.5v when 3 years old
12.3v when 5 to 6 years old and time to replace the battery

12.2v or less is a drained or failed battery

Yes, with key off
B+ stud on back of alternator should show battery volts
As should the yellow wire when 3 wire connector is unplugged
Green wire should show battery volts with key on, unplugged

With engine running ALTERNATOR voltage should be 13.5volts to 14.8volts, 1 to 1.5volts higher than battery volts key off

Battery is not used when engine is running, battery is only used to start the engine then the alternator provides all the power to run the whole vehicle

Alternators have 3 Fields in their case, each Field provides 1/3 of the alternators amp rating, so if its a 100amp alternator then each field provides 33amps
It is not unusual for a Field or its 2 diodes to fail, this is what causes dimming head light at idle(no that is NOT normal, lol)

While I have never seen it myself I guess 1 or 2 fields could become intermittent so you lose 33% or 66% of alternator while driving

I would buy a cheap digital volt gauge that plugs into cigarette lighter, just to check if maybe this is a dash gauge issue and volts in vehicle are not changing

 

Is the cab/firewall to engine ground wire/strap hooked up?

 

All grounds have been check and they are connected. Battery was checked again and it was bad, replaced and truck charged for all of 5 min before same issue. Once the vehicle is warm, with the vehicle in gear the charging gauge drops, but if you give it gas to 1k rpm the gauge shows its charging. The new alternator currently installed is a 200 amp since I am running audio system and several exterior lights. When I got the truck home I checked the battery right away and got 11.5, after the truck sat parked for a few minutes the voltage went up to 12.5, would this show a sign of a bad wire somewhere?

 

Almost reads like someone put an under sized pulley on the crank
It was popular to do a few years back but the problem was, the alternator would stop working at warm idle RPMs because it was turning to slow, cold idle was fine, high, but warm idle, under 1,000, and no charge

No other reason I can think of, the wires are the wires they don't care about RPMs or engine temp, seems to specific to be an "intermittent" issue