So I've had my alternator off two different times, first time I had it tested at autozone, the second being this morning where I took it to O'Riley's. It passed both tests. Now when I hook up the voltage meter to my battery to test my alternator, it has the same voltage while the truck is running as it does when it's turned off and not charging the battery. Has anyone ever had any problems with the wiring? Maybe not a good enough ground? Maybe a hot wire crimped somewhere and cutting off the hot connection? Any info or input is greatly appreciated!

 

is your running test at a higher rpm than idle?
Idle won't charge your battery, more just maintain it.

You should be reading a higher voltage number when the engine is brought up to
I think 2-3k rpm...

Someone else can chime in.

 

You have the same indicated voltage at the battery with the truck off and the truck on, is that right? Should be between 12v and 12.5v with the truck off, and jump above 14v with the motor running. If it's not doing that, meter the voltage between the alternator charge stud and the battery negative post with the motor running. That should be above 14v too - if it matches the low battery voltage, you're looking at a bad alternator. If it's above 14v, you're looking at a bad battery or electrical connection.

 

The other night, I put a fully charged battery on it, drove it 6 miles and even with the lights on bright, I couldn't see anything. The alternator isn't keeping the battery charged. It's been tested twice and it passed so the only thing I see is maybe the alt is grounded out. I've went through two batteries already. Doubt it's because I got faulty batteries. Any idea what I can try to ground the alt to? I think it's grounded on the intake but obviously that isn't working. Would it be better to ground it on the firewall?

 

I would try another alternator. I have read before about alternators testing good out of the truck at the autoparts store but not performing once back in the truck. If you're getting the same problem, then you know to look elsewhere.

 

I think the alternator grounds through the engine block, doesn't it? If you really have a bad ground, then lots of stuff has a bad ground.

But I think you're getting ahead of yourself. Read the voltage from the alternator straight to the battery. If it's low, do a voltage drop test: http://www.aa1car.com/library/voltage_drop_testing.htm

 

In worst case if you need another alternator, check out this link.
I just had to purchase and install a new alternator on my 01 f150 4.6 triton v8 and
SHIPPED it was only $81 from Amazon and it's been working great. It doesn't have
the lifetime warranty that the $180 alternators have from the local store but I didnt see me keeping mine for years to come.
Now its $76

Edit: I should note my other reason for going with amazon was the 30day return period incase the alternator didn't fix my
problem.

 

For whatever its worth my truck was doing the exact same thing last year. Alternator was testing good, and after a new battery and checking everything I went and bought a new alternator. Problem solved. Not saying you should throw parts at it, but if yours is original as mine was, its prob time for a new one.

 

thanks man. Appreciate it. Probly will do that later this week