I have a 1999 f250 been having a problem with the battery light comming on put a new altornator in and a month later the light came back on batteries are also new. If anyone has ideas that would be great.

 

Need more information..
Need to know what engine you have for starters, assuming you have a 7.3 as you said batteries. Single or dual alternator? Please confirm.

Disconnect your batteries from the truck and measure them separately with a volt meter. The batteries need to be at 12.6 volts each, if not charge them with a charger not a trickle or maintainer, a proper charger for sever hours each and separately. Do not put the batteries back into the truck until the can hold a charge of 12.6 volts or greater for several hours after taken off the charger. If batteries do not hold the charge replace them again, or you will continue to have issues.

Visually and physically check your primary cables for discoloration, corrosion, strong mechanical bonding to all lugs.Follow the cables by hand from the battery to the other end. Check the grounds at the engine block, fenders, and frame.

Check the feed lug on the alternator. At the starter solenoid you will see a lug with about three or four wires on it. Two of the wires are about 12 gauge, pull them off and check resistance to the alternator lug. The alternator charges your battery though the two wires which are fused links, if one fails a resistance check replace the entire cable back to the alternator.

Common misuse of a substance called dielectric grease.. DO NOT USE.... Dielectric grease is an insulator and will cause issues. Do not use the red junk for the corner store either. Put all connections back to the way they should be dry or use a compound made for the job (NO-OX-ID). I would also recommend the nice green and red felt battery washers.

After you reinstall the batteries and all connections are made measure the voltage at both batteries. The voltage needs to be as stated above once again.

Disconnect the two wire plug from the alternator and check to insure you have the exact battery voltage measured above on one of the pins. I do not remember which pin off the top of my head however only on and it must be battery voltage.

Start the truck and let it idle for a couple minutes so that glow plugs cycle off. Measure each battery again and you should have 14.3 volts to as low as 14 volts depending on ambient conditions, however they must match. If the batteries do not match voltage check all your feeds to ground and between the batteries again.

A bit **** on the steps but trust me on the procedure.
Let us know what you get.

 

Where did the new alternator come from?

 

Aaand.....
I think we scared him away on the first post.