Have 2005 5.4. Alternator locked up and smoked belt, changed alternator with new NAPA alternator. Battery good, 12.5 with engine off, with engine running measure 14.4 - 14.5. Everything works fine but the battery light comes on at the dash after about 2 minutes of run time. Checked continuity form alternator to battery on cable and that was good. Battery light never came on before. Looked at fuse panel under dash but no listing for anything about alternator, can't find any fuses under dash by battery. Any ideas what could be wrong, alternator seems to be charging with the numbers I got...........any help?

 

Does the battery voltage continue reading around 14-14.5 volts while the light is on?

 

1. Check the connectors:
1.1.the light green w/ red stripe and light green w/ orange stripe wires to make sure it is not damaged and is installed fully.
Light Green w/ Red stripe is the PCM voltage set point for the charging system regulator.
Light Green w/ Orange stripe is the generator load and error condition sent to the PCM.
1.2. The Orange w/ light blue stripe wire.
This is the battery sense circuit

2. Have the new alternator checked.





I would take a SWAG that there is a connector problem with them never being touched in 11 years.
- Make that a WAG, as there is not much science to this pontification, it is mostly Wild A__ Guess.

 

Numbers:
12.15 battery, engine not running
14.51 at battery with engine idling
14.44 at battery with engine idling lights, radio, heater etc. on.

Will check connections tomorrow.

 

replaced Alternator and battery light is still on

 

i have a 2008 & my gen. light has been going on & off for 2 yrs.,have no problems. In cold weather,it never comes on,warm weather it comes on alot but alt. still charging like it should. something is tripping computer saying alt. is not charging,even though it is working fine. look at the needle position on your gauge,see if it moves when you put all your lights-radio-heater on while idling. mine goes to the same position since the day i bought it in 2008

 

That's how its supposed to work, it reads exactly the same as long as the actual system voltage is within the operating range.