The truck is an '89 F250 7.3l IDI

My sunpro gage was only reading around 11v while the truck was running yesterday. While I was waiting on my gf, I had the truck off (because I was on fumes and could spare the fuel idling for 15 mins) I was listening to the radio, went to start it, only had 8v and of course it could barely turn over.

Found out the nut that holds on the alt pulley had come up missing, so I limped her home, pulled the alt off took it into work (I work at advance auto), long story short ended up getting a remaned alt, and bench tested it 3 or 4 times, every time it tested at 15.2v.

Brought it home, put it on the truck, still only doing around 11v. Ended up getting the new regulator and pigtail today, and rewired the whole alt harness, upgraded the charge wire to a 4 gauge wire (I plan to upgrade to a 3G when financially able). The original orange and white wires, I replaced with 14 gauge wire with new ends, ran a new ground (16 or 18 gauge), was hoping to hook it straight to the battery, but made it too short.

After all that work and expense, its still only doing 11.98v at idle and driving.(verified by my voltage tester straight to the battery and alt). If I turn on my heater it drops to right around 10.

So while I'm driving, My batteries are barely charging if at all, I read on another thread that 12.4v and above is charging. Which if I shut it off and go to restart it, it barely has any power and usually wont start without being jumped.

I replaced all my terminals on my batteries, and all the ends on the cables, switched all the ends to copper lugs, and the terminals themselves are marine style.

This truck hasn't been my DD since june so I forget what was normal on it, voltage wise. Any help or knowledge would be appreciated. Would connecting the charge wire straight to the battery be a better solution, right now its running through the solenoid (which was replaced in May btw)

 

What kind of amperage do you have at idle?

Maybe your batteries are going bad and they are zapping all the voltage?

 

Sounds like bad batteries to me.

 

My 92 was doing this, but according to the factory volt gauge, it was overcharging 15-16. However you would shut it off and it would barely crank. It was the batteries. 12.4 is charging, but going down the road you should be around 13.1-13.5 from my experience.

 

most auto parts stores have a tester that you hook up then start the rig and it puts a load on the batts and can tell you if your charging system is working. the big charge wire from alt should be connected to the long post of the start relay, this is where the + batt cable connects also, where is your volt meter sampled from?