techrep

iTrader: (1)

With a multimeter... do what mark told you to do.. fire it up and read DCV on the battery while it’s running.. should be 14+VDC... if not alt is bad.

05F1504x4

Only alternators I can get my hands on is a New Duralast Gold alternator or an Ultima 110 Amp Alternator (Remanufactured)

On the multimeter the battery- just keep the jumper cables on when I doing it or take them off. Let it die and then get the read.?

Wesley416

Put the leads of the multimeter on your battery start your truck then remove the jumper cables and see what it reads if below previous stated voltage your not charging. If you leave the truck connected via jumper cables youll not be reading what your trucks doing but rather what the other truck is doing or a combo of both good luck

05F1504x4

Alright put the alternator back on and put the multimeter on it. Results-

5.26 with just battery won't turn over.hold key on- falls to 0.92 -off the key 5.05
Put jumpers on it goes up to 13.5ish but wont crank until let it charge for a few minutes until it's up to 14ish. Cranked up fine.
Disconnect the jumper cables and it stays running instead of dying like before.. @ around 13.97-13.99 with lights on. Lights off its &14.01
I turn it off and the voltage starts falling from 14 to 12 instantly the After a few minutes the battery is back around 5.77.

Is this the alternator or the battery?

Wesley416

Try this to start eliminating things work battery to alternator. Charge your battery and take it to autoparts store and have it tested some stores will charge it for you if you dont have access to a charger but it has to be charged to be tested. Based on your alternator multimeter test I'm leaning towards battery but based on your first post it could go either way if battery tests fine alternator seems suspect if battery is bad well there you go. Good luck report back take care.

05F1504x4

Ok I'll get that battery checked tomorrow. Battery is definitely cheaper than an alternator.

redfishtd

alternator needs a good battery to accept charge . Batteries only good for 3-5 years -- heat kills them .
If battery not willing to kick into system alt will not be able to handle all loads .
you also may have a phantom load killing your system --draining it .

05F1504x4

Yeah I have seen all the post of people having parasitic drains on 04-08 f150s and not being able to locate them. I never knew it was a very common thing with these years

digitaltrucker

In the old days, you could start a vehicle and disconnect the battery. If vehicle continued to run , alt was good.

As stated earlier, you are going to need an alt and i also believe a battery. If you jump it and it dies, to me, alt is not producing correct output.

Is this already a third party alt?

techrep

iTrader: (1)

What’s the installed date on the battery ?