Hey ya'll, in a bit of a pickle. Battery light comes on when the truck is running at less than about 1200rpm,but i see zero movement on the needle.
Weird thing is i charged the batteries and tested the alternator with my multimeter and it was reading 14.1-14.2 which is nominal. Run it for about 10 min then it reads 12.3-12.8
I'm thinking a bad cell in the battery or alternator is going out. Oh and all the connections are tight, wires look good.
I'm not sure, any suggestions appreciated.
01 f250 4wd 7.3 intake exhaust basic tuner guages
Oh yeah, live in Fl, could the constant heat be a factor?

 

With engine off
Pull ground on one battery and then after an hour check voltages on both batteries and report back. If not equal you have one pulling the other down.

Start it with both batteries connected and disconnect ground on lower one. See if volts are OK after running it a while and alt light don't come on.

Or bring both to a batter place to load test.

 

See this post.....

https://www.ford-trucks.com/forums/1...tor-issue.html

 

You can easily check each cell in the batteries by using your VOM. Start by attaching one lead to one post and the other lead into the adjacent cell to measure its voltage - should be 2.5 v, then put the lead from the post into the next cell and read the voltage. Continue this until you get to the last cell with one lead on the post and the other in the last cell. If any cells read low, then that's a possible dead cell even though you may read 12 v across the two posts.

 

While you're checking everything else, attach a multimeter across the large posts on you Air Intake Heater and Glow Plug relays to see if you have a voltage drop or not. If you read full battery volts across the large lugs on both relays, then they are inactive. If either one of them shows zero volts across the studs, then the one with zero volts is active and sucking the juice down.

In my case... my alternator would allow the voltage to drop, and replacing it took care of the problem.

 

A fellow Floridian. Pull alt and have a local auto electric shop test it. While your in town have your batteries load tested. It is probably alt, but a bad one can also kill your batteries.

A good load tester is a great tool to own!

Good luck!

 

Every time I have had the Batt light come on, it has been alternator related.

I agree with what has already been stated... Have the batteries load tested, and you can take the alternator in to an auto parts store for them to bench test it.

 

None of my battery issues every brought in the battery light. Even when my starter went bad and killed my batteries the truck wouldn't start without help. It was so bad that I had to disconnect the batteries to get a jump from another diesel with two batteries and an HD alternator. Even when I hooked my batteries back up my original alternators (over 10 years old) could still put out ~13.5VDC at idle.

 

Same here.

 

It won't. It really is an alternator light. 95 percent of the time it only comes on when the alternator is not functioning properly. The best way to protect your batteries is a cheap little plug in meter that goes into your cigar lighter that shows raw battery voltage before starting. You can catch a problem early checking that daily before a problem, starter, alternator or slow drain, takes them out.

 

I've got battery voltage on one of my pages in Torque Pro. It is not a normal parameter I monitor but now it will be after my alternators finally giving up. I can't complain, though. The truck was built in July 2002 and these are the original alternators. 14 years in SoCal and a lot of off-roading with underhood temps reaching 140F in the summer.

 

Those little plug in gauges for the cigarette lighter are one of the greatest inventions. You can get them for under $10 on Amazon. I keep mine in the outlet and plug it in before starting my truck. My mechanic buddy has had one for years that he uses more often than a multi meter on customers cars and his own.

 

Yup, x 2.. you will have all kinds of answers if you do this. And it is free. And in my case, it is only 10 minutes up the street. Pop out the alternator , batteries and take up. Easy peasy.