Ronald asked about the charging system in his 2003 2.3l Ranger in a Conversation note
Easy to test with a volt meter
Batteries last 5 to 7 years, they run out of chemicals to hold a charge, and can also become self draining if a plate inside shorts out
We will come to that at the end
Key off, set Volt meter to DC Volts
Test battery voltage first, say its 12.5volts(3 year old battery)
On the back of alternator is the B+ terminal, should be a Black/orange stripe wire, do not disconnect it, test voltage using alternators metal case as the ground, should see 12.5volts, if not then Fusible link has burned out
Unplug the 2 wire connector on alternator(3 wire on V6 engines)
Test Yellow/white wire, should see 12.5volts, if not fusible link is bad
Test Light green/red wire, should be 0 volts
Turn on the key
Re-test wire, should see 12.3-12.5volts, if not fuse 11 in cab fuse box is bad, this is the ON/OFF switch for alternator, also Battery Light wire
And thats it, if the 3 wires test as OK then truck wiring is OK
Plug the 2 wires back in
Start engine
Re-test battery voltage, should be above 14 volts just after start up, if not alternator is bad, for sure
Battery test
Unhook one battery cable
Test battery voltage, write it down or remember it
Re-test voltage after 4+ hours, overnight is best
If its lower, under 12.3volts, then battery is self draining and needs to be replaced
New battery is 12.8volts
3 year old battery 12.5v
5/6 year old battery 12.3v, shop for battery sales
12.2v or lower is a done battery, could just be drained from bad alternator, so re-test after a few days of driving with new alternator, BUT...........test it in the morning BEFORE starting the engine, just after shutting off the engine any battery will show a "false" higher voltage for a few hours
A bad battery can cause alternator to fail
A bad alternator can cause a battery to fail
So not uncommon to have to replace both at the same time
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