BrokefixinmyFord

F150, 5.4 w/ac, 135,000 miles on it, driving down the highway and radio, all gauges, lights go dead. When I put it in park (in a restaurant drive through) it locked all the doors and would not come back out of park. I got a jump, ran across the street to a parts shop and bought a new battery so we could then check the alternator. Battery was 9.6v at this point. New battery, cranked right up, tested alternator and got 12.5-12.6v is all - not expected 13-14v. Ran fine, showed slightly positive on battery in dash. Today, drove it a little and as I came home it powered down in parking lot of parts store - where they charged the battery and I bought a new alternator. Now I get a battery light - haven't seen that before. What is it...why me...now with a good starter, a new alternator and a new battery, why the battery light? Any help out there?

supercrewzn

Have you checked to make sure battery terminals are tight? What about solenoid on firewall? There is also a couple of relays and fuses you can check. I dont know where they are for sure, as I on an 02. Someone can chime in and tell you that info.

tekmunki

^

Loose/corroded cables, or possibly a loose belt. Loose connection on the new alternator is another possibility.

After checking that- if it were me, I'd drive it back to the parts store and recheck the new alternator and battery; defects happen. Not to mention running a new battery with a bad alternator can sometimes to bad things to the new battery.

60DRB

First, most national name parts stores will check/diagnose your charging system and/or battery for free. After checking all cables and connections for faults, if the (new) battery is not getting charged or keeping a charge, I would suspect other things. You already replaced the alternator. Has the voltage regulator been checked? On some makes the regulator is imbedded in the alternator. I'm honestly not sure if that's the case with our trucks, but I doubt it since the new alternator didn't correct the problem.

techrep

iTrader: (1)

Ground !!!

sjoholm

If that battery wasnt fully charged when you changed the alternator you could have fried that brand new alternator. I have been a victim of doing that before.

BrokefixinmyFord

Ok, I have gone back to A-Z for my post install checks - battery good, alternator good - output 14.1V under load goes to 13.6 (air, lights) but I still have a battery indicator light on the dash. I was told by a Ford guy that non-OEM alternators are "built wrong" and won't send the right "message" to the voltage regulator hence the light. I did notice last night driving home from work the headlights seemed to go a bit dim then strong again on occasion. I just don't want to be stuck somewhere (and somewhere for me can be just about anywhere). Any more idea? The one on "ground" seems plausible but ground what to what?

tekmunki

If you tested out OK, I'm still banking on a loose connection or corrosion.(possibly in the ground)

This guide would be a good way to insure ample (pun intended) power and grounding. Not to mention reducing the resistance may clear your battery light.
https://www.f150forum.com/f33/how-big-3-upgrade-46822/

btw- I might have missed it, did you check the belt tension?

jmw27403

so i have a question im attending a automotive and diesel school, last week we were covering alternators. our electrical teach asked a bonus question.

there is a truck in a field, for this "exercise" its a 1989 ford f150. it has EFI, and it has no battery. so three guys go out to the field and push it out the field. they got it up to 20mph and popped the clutch and it STARTED!!!! how the hell did it start. remember you need to induce field current for it to work. the battery cables are hanging if they touched the sidewalls or each other it wont work.

rick99601

the harmonic balancer pulley on the crankshaft runs your accessory drive belt which spins the alternator creating current.

if you get going 20mph and release the clutch (in at least 2nd gear going that fast) you've just done the same thing your starter does.

you need to be careful running without a battery hooked up on newer cars though since the battery acts as a buffer so voltage/current spikes dont harm the ecm.