Rat ate wires at alt, repaired the wires. and it charges, but the battery light stay on.

Did you have the charging system diagnosed or did you just guess at it being the alternator . The charging system is computer controlled . The starter isn't working because low power , battery dead . Is there B+ voltage at the wire on the back of the alternator .B+ voltage at pin 3 at the connector pluged into the alternator .
Charge the battery use a volt meter an test for B+ voltage at the places i mention . No check engine light ? DTC'S - diagnostic trouble codes stored .
Ford Smart Charge System Alternator Not Charging
Ford PCM controlled alternator testing

The Charge lamp comes on with the Alternator fails to keep battery charge going. (lots of way to fail, and ALT Is 100% good) it's a system. each part of it must be good, end to end.
so...
i put my voltmeter across battery, i start car, i see 13.3 to 15vdc, alt is good.
no? , i see now, 12.2v. ALt is dead, (i didnt say bad) and battery is sightly discharged, 12.6v is charged. (key off, rested voltage)
This 12v tells me the ALT is shut down. only why is the question.

how can any charge system fail,
bad battery tops the list here, they LOVE to fail.
1: belt slips.
2: belt missing
3: bad alt.
4: bad wires to ALT . (corrosion on any wire or lug)
5: fuses blown , any listed below.:
your alt is not an ECU controlled, alt ,its 100% self contained

did you ever remove the ALT and blow the 100 amp fuseable link
the first step of any alt pul, is the pull the NEG, battery lug or BOOM.

im logged in to alldata.com so can you.

and what do i see.
a 5 wire ALT. one is the frame ground, so it must not be rusty or..... it fails. frame to engine block. no rust here.

wire L , yellow.goes to dash LEDs (alt failure idiot lamps) (this works)
wire. S white goes to ALT 5a fuse, is it blown?
wire :B B/G color, goes to the 100 amp link fuse. (blown>?)
wire IG Red-white, goes to a fuse marked 10A gauge.

i think the IG wire is the voltage sense wire.
no sense, no charge. I think the whole I/P dash cluster goes dead when this fuse blows.

The S wire is the boot strap voltage sense, it wakes up the regulator .
if open , the reg stays asleep, as does ALT.
Alternators can not self start, the regulator has boot strap device
that cures that. called self excitation. so this wire is critical.
All wires except the L wire is critical. in this case.

the B wire is the big wire, it charges the battery . 50amps or more..

any of the 5 paths open , kills the ALT dead.
The REG inside the ALT can also shut it down.
eg: battery bad, with huge cell resistances. total.
eg: overvoltge for any reasons. including attempts top run car with no battery, (dont ask)
eg: over current (battery cells 1 to 6 shorted) or 25 KC lamps added.
eg: over temperature shut down.

that is about it.

you may have a problem with the ecm(computer)that is causing your problem.you also may have a defective alternator even if it was new one.

The alt should charge at around fourteen volls , any ways, yogi need to put another battery. A weak alt will kill a good bat.and vise versa

Check the drive belt tension and wiring connection at the alternator and at the battery. Check for a blown fuse in the fuse block . -hope this helps

Check the small wires that clip into the side of the alternator, they set the Field coil in the alternator and could be causing the issue. Also, how old is the battery? If it's bad the alternator will cook the voltage regulator because it will be at max out put all the time.

Review in autozone.com (free register), there you can find 31 Wiring Diagrams about F250.



Good luck (remember rated this help).

No, They are unrelated in that sense. But, The not charging and bad battery will affect the warning lights. Ck the charging voltageee at the battery posts, Chargr rat is between 13.6 to 24.2. iF THE BATTERY IS BAD IT PROBABLY WASTED THE ALTERNATOR hAVE BOTH BATTERY AND ALT TESTWD

Check all fuses, both inside and outside. Use a volt meter to check the output of the alt., by setting the meter to D/C/ volts, put the black wire on battery GROUND and the red wire on the big terminal of the alt.,,, which the wire is held on with a nut and washer, or a lock nut.If your reading is around 12.0 - 12.6,,, try another alt....
If the reading is 13.8 - 14.6 ,, you have a problem between the alt and the battery.
Hope this helps.

check the module on the firewall where the wires connect using a circuit light. Also check for burnt fusible links and wires connecting the battery, module, and alternator. A grounding power wire is most likely the culprit.