Battery Issue
 

So this all started a week ago when I helped a guy jump his car. He crossed his wires and when I connected mine it zapped the truck. Worked normally for a week. Now while driving my battery light on the dash comes on and it turns off the ac. When I get it above 2000 rpm driving the light goes off and will come back when the rpm drops. This morning thought the battery was dead. Cleaned the posts of buildup on both batteries and started fine. But the battery light and ac issue is still there ... Hooked up a scanner the other day and didn't pull any codes. This is a 2001 and it has dual alternators. The belt is a little worn and I'm already planning to replace that because I believe it is the original. Any help is much appreciated!

Can you check the output of each alternator independently when the truck is running?

Both were fine. Right side was the side that got zapped and it had 12.2 volts and the left had 12.0.

The running output for each should be 14.1v

Would that 2 volt difference cause those problems though? So does that look like an alternator issue then? What is the alternator output and how could I check it?

12.2 and 12.0 are two dead batteries. Even with truck off after sitting overnight your batteries shouldn't read that low. If that's the voltage with it running then both alternators are most likely blown. I would start by removing the alternators and have them tested at your local autopart store. Also charge the batteries before you install a new alternator. There also may be a fuseable link somewhere in line that may have burned out also.

Out of curiosity should I look at switching to the single heavy duty alternator or is the dual setup better?

I would stick with duals.

Have you made sure all three fuses that supply the field currents are intact?

Fuses #5, #6, and #7 in the under-hood fuse box (battery junction box). Number 6 is a 10-amp, and the other two are 5-amp.

Below is the layout of the fuse block, and a PDF of the charging circuit wiring diagram.

Pop

Just changed my batteries Sunday. One read 12.2 and the other 12.1 .; It was starting harder every day for a week, now its runs great. If you do buy batteries buy the biggest you can find. My motorcraft lasted 4years and 10 months. I went back with interstate like before that lasted over six years. Found a sale and they had 20% off that thur sunday. Lucked out. It didn't want to start Sunday morning.

The 2 batteries are wired together inline, so if one got zapped, the other one did too.

Using a voltmeter, measure the voltage on the battery posts while the truck is running. It should be +14v.

But be sure and check those fuses....maybe you got lucky.

While getting the alternaters checked out I would get the batteries load tested also just to make sure their up to par.

Already pulled both alternators and will check fuses when I get home. Also noticed a tube about the size of the dip stick tube above the lower alternator. It's open on the bottom and can't see where it goes. Looks like maybe into the block? Does anyone know what this tube is and if so should anything be connected to it?

Sounds like the drain tube for the fuel bowl if it's the one that's open. There is another that goes from the passenger's side manifold to the Exhaust Back Pressure Sensor(EBPS)

The tube to the exhaust manifold is still intact. This tube is between the lower alternator and the block. Has a 45 degree ish bend and by hand I can jiggle it up and down about 1/2". Replaced the alternators and now reading 14.4 idling on both batteries. Next is replacing the battery cables. Worn out and I don't think the connection is as good as it could be ....