We have a 2003 F-350 that we bought used last year.
Everything was fine until about 4 months ago when the battery light started coming on. Alternator tested OK, so we bought a new battery.

That wasn't it because the battery light came on the very next day.

The most puzzling part of this is the gauges will sporadically peg out and then go to 0, then go normal. It has done this as much as 8 times in a row and other times it doesn't happen at all.

Then the passenger door lock stopped working for about 3 weeks, then suddenly started working.

Someone suggested it might be the Voltage Regulator, but from what I've read so far, it is part of the alternator...??

Any help with solving this issue would be greatly appreciated!
This is the truck we use to pull the horse trailer and have been too afraid to do so since this all started.

Is has an electric brake controller installed if that might have anything to do with it..??

Thanks!

 

How did you test the alternator? Voltage reading at the battery running with fluke or other voltmeter? And what was the reading? Did you take voltage reading at battery when your trying to start to see how far down the battery drops, this will indicate battery status. Gauges pegging is a battery dropping down too far in start load. The door lock issue would seem unrelated to battery light. How long has light been on ? constant? does truck sit alot? daily driver? Battery cables in good condition ? terminals? voltage reading at battery off idle (rev)?

 

If all checks are ok do a battery drain test to see if your battery is getting too much draw on it sitting, taking life out of battery, when truck is off wait till cpu goes into sleep mode, amp draw on battery will only be enough for cpu memory and clock. should be around .5ma

 

Your alternator is intermittently failing to charge.

It should be less than 50 mA, not 1/2 of 1 mA.

 

Yes, we tested with it running at the batttery with a voltmeter. Once at the dealership and twice at Advance Auto Parts. Only remember the reading was normal. Advance Auto did the whole nine yards with it running and stopped and re-started and off idle at rev. He had a whole procedure he went through.
I understand what you're saying about the gauges, but they don't do it at start; they do it as we are driving down the road - always.
The light's been coming on for about the last six months. Sometimes it comes on and stays on and sometimes you drive a ways before it comes on and it might go off intermittently.
Battery cables and terminals are good.
The gauges going crazy while driving is the most puzzling part to me. Haven't read anywhere the alternator can do this.
Thank you both for your replies.

 

The gauges were deigned to do that when their supply voltage drops below a certain value.

Therefore, either the supply voltage is dropping below the threshold or the cluster has a defect.

 

Thank you all for your posts.
I think we will just change the alternator and see what happens. Hopefully it will cure the problem.