About a year ago the vehicle wouldn't charge, and I found the burnt fusible link in the wiring harness leading from the alternator to the battery and replaced it with like color and gauge; everything was good for almost a year. Recently the battery light came on and the vehicle eventually died. I charge the battery and started the vehicle and checked the volts. All around I had 12 volts, but the battery eventually drained down and battery light was still on. I then replaced the battery and alternator, upgraded all the grounds and positives to lager gauge wire, re-soldered the fusible link in, and checked all the fuses (all good). The battery still drains, the light is still on, and the volts read what ever the batter is (back feed).

When I check the alternator I check the hot to ground, the casing for ground, the battery itself, and the power to the fuses.

Any help would be appreciated!

 

Welcome to the forum

3 wires to check for the Vehicle side of the charging system
Key OFF
B+ on back of alternator should show Battery Volts, thats from the fusible link you replaced, but there are 2

Unplug the 2 or 3 wire connector on alternator
Red(or yellow) wire on 3 wire plug should show Battery voltage, this uses a different fusible link<<<<

Grey(or light green) wire should show 0volts
Turn key ON
Grey wire should now show battery volts, maybe .1 or .2 lower with key ON, this is the Battery Light circuit and also the ON/OFF switch for alternator

If it has a purple or white jumper wire make sure its connected and not frayed

If all voltages test OK, plug connector back in and start engine

If you don't see above 14volts at battery then replace alternator, new or not, its bad

Diagram below

 

No luck, everything checked out; B+ and three prong red, read batt volts, grey reads 0 volts when keys is off, and then batt volts when on. I also replaced the alternator (good thing they're only about $100 bucks) and it still won't charge. Volts continue to drop, I'm down to 11.5 reading on batt and B+.

 

Is the Battery Light on with key on and stay on?
And does it stay on after engine starts?

I would stop buying alternators, just take it back until you get a good one

If the wires test OK, then alternator IS the problem, new or not

Ford does have a battery monitor circuit in the HEC instrument cluster, part of the old "smart charging" setup they used in the early 2000's
I can't see that being the problem on a 2008 Ranger but........................

Google: ford smart charging trouble shoot

 

Yes, the battery light comes on and stays on. I'll google that. Thanks for the help. If I ever figure it out, I'll post an update.

 

There really are only those 3 wires in the Vehicle side of the charging system, so if they test OK then its a bad alternator if battery light stays on with engine running