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Tim Mohr
Category: Ford
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Battery light is on on my dash. Battery eventually died

Customer Question

Battery light is on on my dash. Battery eventually died while driving.
JA: Have you checked the fuses? Have you tested the dashboard light bulbs?
Customer: Dashboard light bulbs?
JA: What is the model/year of your Ford?
Customer: The bulbs are on
JA: What year is your Ford?
Customer: 2008 Ford Ranger
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: 4.0 4x4
JA: Anything else you think the mechanic should know?
Customer: Yes, I was hoping to fix myself. The alternator was tested as good. Battery is brand new. Tested resistance on the cable between alternator and battery and it was good. There is a 3 pin connector and a single pin connector on my alternator. Red, Purple and Grey. Then a single Purple
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Ford Mechanic about your situation and then connect you two.
Submitted: 3 months ago.
Category: Ford
Expert:  Tim Mohr replied 3 months ago.

Hi, my name is ***** ***** you remove the 3 pin connector and see if the grey wire has power on it, with the key on?

Customer: replied 3 months ago.
Hey Tim, already done a bunch of trouble shooting. The grey wire and red wire in the 3-pin connector have power to them
Expert:  Tim Mohr replied 3 months ago.

Ok, with it running, what is the voltage on the large red wire, at the alternator?

Customer: replied 3 months ago.
The one on the post that is intended to supply the battery? That would be the same as the battery. Currently about 11.9 while running. Decreasing the more I run the truck
Expert:  Tim Mohr replied 3 months ago.

ok, then you have a bad alternator, all you need to charge is power on the big red wire going to the battery, and power on the grey wire and the small red wire, how ndid you s=test the alternator?

Customer: replied 3 months ago.
It's not the alternator. It was bench tested at the parts store AND I tried a new alternator just to be sure.
Customer: replied 3 months ago.
This is why I've come here. I'm fairly knowledgeable. But this one has me stumped.
Expert:  Tim Mohr replied 3 months ago.

the only other thing that can cause it not to charge, if the alternator is good, id the ground on the alternator case, have you checked to see if the alkternator case shows a good ground?

Customer: replied 3 months ago.
tested the ground from the alternator. even added a temporary ground wire to it just to be sure.
Expert:  Tim Mohr replied 3 months ago.

ok, can you double check the grey wire at the alternator, and make 100% sure it has power when disconnected, and also mak sure it does not show a short to ground?

Customer: replied 3 months ago.
I'm 100% sure about it having power but I will go confirm there is no short to ground. be back in a minute.
Expert:  Tim Mohr replied 3 months ago.

let me know,Tim

Customer: replied 3 months ago.
it definitely has power. How do I test if it has a short to ground? That wire goes through the dash light bulb, so it should be grounded at some point no?
Expert:  Tim Mohr replied 3 months ago.

if you disconnect the connector from the alternator, and start it, is the battery light on, or off?

Customer: replied 3 months ago.
off. that battery light is in the same circuit
Expert:  Tim Mohr replied 3 months ago.

yes, power is supplied to the light in the cluster, and then goes to the alternator, where the diode pack grounds it to turn on the light, this wires also excites the voltage regulator inside the alternator, if it has power, and the light does not come on when the connector is removed, it means the wire is not grounded between the light and the alternator, and this just leaves a bad alternator, nothong else, where did you get the new alternator?

Customer: replied 3 months ago.
That makes sense.. except the alternator part. I had my current one tested, as well as purchased a new one to be sure. I bought the new one from partsource.
Expert:  Tim Mohr replied 3 months ago.

but you have done every test, and it came back all to the alternator, this is a simple system, it requires power on the grey wire, the small red wire, and the large red wire, nothing else to make it charge, so it has to be a bad alternator, when bench testing the system, they put power on all three of these wires and ground the case and you have checked al these and they are all correct, so this just leaves abad alternator,Tim

Customer: replied 3 months ago.
I can't see how that would be the issue. But I will try buying yet another alternator and get back to you.
Expert:  Tim Mohr replied 3 months ago.

let me know,Tim

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