The battery light came on today while I was working on/driving my 1994 F350.
I cleaned both terminals.
I removed the negative cable while the truck was running and it kept running without any problems or changes.
With the truck off the voltage on the battery is 12.44
With the truck on the voltage on the battery is 14.14

Truck starts without any problems. What is the battery light trying to tell me?

 

Test voltage with the truck on again. Rev the engine up as you do so. Make sure it doesn't go any higher than 14 volts. 15 to 16 is getting to a not so good range.

It could also be that this has nothing to do with the battery/alternator voltage but a short in the cluster.

What were you working on when the light came on? Anything else happen?

 

I think it came on after I removed the negative cable from the battery for an hour. I was trying to reset the pcm. I have been checking vacuum lines, spark plug wires, and fuel components. I will go see if I moved some wires around on the alt, I already checked it but I will check it again.

 

If the battery has correct voltage (engine off test), and alternator passes also (engine running test) then I'd ignore it and see what happens honestly.

Usually that light will indicate a charging failure, ie alternator not putting out correct voltage while the truck is running. If you're saying that's not happening, I'd ignore the light haha.

Uh, did you do anything else to the truck besides disconnect the negative cable?

 

I just went out and re-checked the voltages:
12.14 with the engine not running
13.33 with the engine running at idle
13.39 was the highest it got while holding the throttle half way open

I have to drive the truck tomorrow. I put an extra (good) battery, the voltmeter, and a set of jumper cables in the back seat. Just in case.

I am actually replacing the instrument panel this week, so we will see if it is the gauge cluster short or if the battery light stays on in the replacement.

 

Battery light's on because the alternator is failing. Not the battery, but the alt.

13.3 is UNACCEPTABLE. Yank the alt and go get it tested, or try and test it yourself again later.

The alternator's still working at this point, but it should be putting out at least 14 constantly, you're not running on battery alone just yet, but you're on your way.

 

Alt is bad, replace it.

 

I drove it 90 miles so far. The battery light was going off and on the whole time. I will have the voltage regulator checked on the back of the alt today.

 

Good man. If can just get the entire alt checked, not just the regulator.

 

This afternoon the light never came on. It went 45 miles and at least 10 red lights, plus 1 stop to at the store. No battery light issues this afternoon so I did not go to the auto parts store.

 

I guess whatever floats ya boat my man. Your tests say the alt is dying. If you're not gonna test it or just replace it, monitor it. However, even that will not prevent it from dying whenever and where ever it wants to.

 

yep. by it not charging fully not only is the alternator dying but its slowly killing the battery also. if you continue on like this you'll be replacing the alternator and battery.

 

Its def a bad alt. Altho, some parts stores will tell you it tests "good" it is not. I had a rebuilt lifetime warranty alt have low voltage after it was warmed up. The tested it with it on the pickup, told me "its good still" it was charging at 13.6 volts. Needless to say, if I had the lights on , and the blowEr motor on hi, it was discharging the battery. The next time I took it to the store to get it tested, I had all the lights on the A/C on, and it in reverse(with the parking brake set) and it failed. I got them to give me a higher amp alt for the warranty exchange.


Just replace your alternator. It will save a headache later on.

 

Sounds like the belt may be slipping. Check your belt tension device.

Also NEVER removed the negative cable while the truck was running, this make electronic devices go bad as the voltage can spike over 100 Volts.

You never want to clear your codes by taking off a battery cable either as this can also cause problems and set a code. Clear codes with the STI wire, and when the MIL starts to flash take the ground away from the STI wire. The codes will be cleared.

 

X 2 on the belt , to test the alt you need to test it with a vat-40 or simalar , needs to be under a load to tell the alt output....Lew