02 2.3l 5speed

My alternator went bad supposedly. My brother replaced it and his ex-wife used the truck for about a week until I had issues with the ircm.

I get the truck back and it's charging at 17.5v obviously way too high. Brand New alternator. Pull it, get it tested, comes back within specs.

I fixed the ircm **** and put a different alternator in the truck that also tested out within specs.

Seems to be holding at 12.5v with the truck on and running. 12.34v with the truck in acc. And 12.42 truck to off.Drops 11.85 with ac and lights on.

Where do I go from here? What is the next step to troubleshoot this problem?

 

Alternator is not working at all if voltage is under 13.5v engine running

Car Batteries should be
12.8v new
12.5v 3 years old
12.3v 5/6 years old, time to shop for battery sales

12.2v or less is a drained battery or bad battery

When you start the engine the alternator's internal voltage regulator will output 14.3-14.8volts, for fast recharge after battery was drained by starting engine, this only last for a few minutes, as over 14volts will fry a car battery long term
So after engine has been running a few minutes system voltage will be 13.5-13.8volts for the rest of that drive cycle.

So your engine running voltage of 12.X means alternator is not working
Quick look, does the Battery Light come on with Key ON, it should, that's the ON/OFF switch for alternator, if no Battery Light on dash then check/replace fuse 11 in the cab fuse box

The should be 3 wires on your alternator
Test wires, Key OFF, test battery volts now, that will be used to compare to wire tests, lets say its 12.3v

Larger black/orange wire connected to B+ on the back of alternator, use alternator's metal case for the ground and test this wire for 12volts, it should show 12.3v(battery volts)
If not then Fusible Link in wiring harness is blown

Unplug the 2 wire connector on alternator, that's the Voltage Regulator, just FYI, its 3 wire on V6 models
Test Yellow/white wire, should be same as above, 12.3v, if not then Fusible link is blown

Test Light Green/red wire, should be 0volts
Turn key ON
Test wire again, this is the Battery Light wire, should now be 12volts, doesn't need to match battery volts exactly, key is on now so there will be a drain on battery
This light green wire is the ON/OFF switch for alternator, so important
As are the other 2 wires

If all wires test OK, and engine running shows under 13.5volts then alternator is bad, period, doesn't matter what test they run, its bad, charging systems are NOT complicated

If you did see 17volts engine running then battery is most likely cooked, and you could have blown some of the fusible links
Fusible link is just a 6" wire that will separate, like a fuse, if AMPs get too high, they are used instead of a fuse because they can tolerate spikes in AMPs without blowing instantly like a fuse will, so they are "slow blow fuses"
They will be near the battery end of the alternator wiring, usually wrapped up in the wiring harness