1996 ford f250 diesel truck alternator

If the battery is being drained while the engine is running it can only be because the charging system isn't charging or isn't charging enough.

When everything is working correctly the alternator supplies all the current the vehicle needs with a comfortable surplus that keeps the battery charge level topped up.

If the charging system is working correctly and the battery is becoming discharged while driving - the discharge fault would be so huge the result would be smoke and fire. As that isn't the case the obvious conclusion must be a charging system that is defective.

I would reccomend you go back to the alternators again. Have it tested. There are many bad parts going over the counter these days, and I have replaced"new alternators" 3 times before getting a good one.

Check the wiring on the Alternator leading back to the Firewall. On some models there is a split in the wiring and one side has a fusible link on it. Sometimes the wiring rests on metal parts and wears through from vibration. Check for this and tape the wires to avoid the rubbing.

Ford in the past has put fusible links near the Batteries and when the Batteries are removed, the wires are brittle and possibly corroded. Its just a matter of failing a little earlier from being disturbed than from corroding through. Check all of your connections.

Make sure your Batteries are fully charged. They should be at 13.2 to 13.4 Volts. I know of an increasing amount of Ford products having charging problems immediately after a Battery switch.
Alternators have stopped charging while the vehicles are on the E-way. The charging systems are being disconnected by something built into the vehicle. I suspect the Anti-theft or Battery-saver systems.

I hope my solution helps you.

Just a thought.......... If the alternator is not grounded properly to the chasis , it will not charge , and the charge light probably will not come on either. Check for loose , or corroded ground wire or strap.

The next logical part to check would be the Battery!!!!!!

could be vacuum pump. check for vacuum at line into booster (should be significant). if not ok, check for vacuum at pump to make sure it is not a line problem. if there is a check valve in the line, ensure it is working.

Thats a guessing game, but first, if the battery light was on, that means no alternator output. So recharge the batteries and be sure they are good, Then replace the alternator. If the batteries and the alt are good, and the battery light is off, then all should be OK.

wont charge what? If you are talking about the battery have you had the altenator checked or checked the fuses, battery terminals, and cable corrosion, or lose connection.

Charge the batteries. take a Reading to make sure that you are getting almost 14v to both batteries. If it is not charging then take the alternator back off and have them check it. you might have bought a bad one. There is a way to test the glow plus with out taking them out. ( Take a piece of wire long enough to reach all the glow plugs from the battery. unplug the glow plug wire.If you touch the end of the glow plug with the hot wire it should make a little spark. if no spark then the glow plug is bad. do this to each one, but one at a time)

Hi, seems that your alternator diodes are faulty.
You can check this by disconnecting the radio & switching off all interior lights etc.
Then remove one battery lead.
Then get an amp meter and connect it between the battery & the removed lead.
If you get a reading the alternator is drawing current , hence faulty diodes.
The alternator will still charge the battery when the engine is going but then discharges when stopped.
Also check your batteries with a hydrometer by checking the battery acid in each cell as you could have a dodgey cell in them.