This one is weird. Been having charging problems. I belive its tied to the circuit that has the dash light. This light when you turn the key switch but before starting will flicker on and off and sometimes won't come on at all. Where does the power to This circuit come from? Alternator and battery are fine. But without power to This light the truck will not charge.

 

What year Ranger?

Yes, the Battery light circuit is the Startup Voltage needed first so alternator can start to generate voltage as is spins
(Alternators need startup voltage, Generators do not)

battery(12v)-------ignition switch---------fuse--------------battery light bulb-------------------------------(light green/red wire)--------------------voltage regulator in alternator

Fuse was used in 1995 and up, not before

The way it works is that the terminal that the green/red wire is hooked to on the voltage regulator in the alternator is "like a ground", the I terminal
So with key on the battery light bulb has 12v and "a ground", so lights up
That 12v is passing thru the bulb to voltage regulator which uses it to power the rotor, simplified
When engine starts alternator is now producing at least 13.5volts
So bulb has 13.5v(not 12v) and Voltage regulator is also at 13.5volts, if both terminals on the bulb are 13.5v then bulb is off, no electricity can flow thru the bulb
If alternator voltage drops below Battery Voltage then battery light will come on, alternator is failing

Simple test
Unplug the 2 or 3 wire connector on alternator, use a jumper wire to GROUND the green/red wire
Turn on key
Battery light should be on and steady, no flickering
If so turn key off, remove jumper and plug connector back in
Turn key on
See if its flickering, if so Voltage regulator in the alternator is the issue

If it flickers in both then could be the green/red wire or an issue in the cluster

 

Nt

 

2009 has a digital dash, so cab fuse box fuses 9 and 10 are used

And its a GREY wire on alternator's voltage regulator, green/red wire was used from 1989 thru 2006

So jumper the grey wire to test