I have a 2005 PS that has 72000 miles on it. Yesterday as the day progressed, and I had to start my truck multiple times. It seemed to have less power and was harder to start each time. Until finally I had to get a jumpstart, I took volt readings and both batteries were low (8-10 volts)
I then took a volt reading off the alternator and it was only 12 volts. Is the alternator supposed to put out more volts? Could this be something else causing the problem? Any knowledge would really help before I pull the alternator to have it tested.

 

Alt. should be putting out 13+ volts after the glow plugs shutdown. App. 30 to 60 seconds after start up. If not , the alt. is going out or you have a shorted cell dragging it down. How old are the batteries? If you have them tested make sure they are disconnected from each other or you will get a false reading.

 

When you say harder to start each time, do you mean it longer and longer to crank even though it was warmed up? If so then I suspect you may have a high pressure oil leak somewhere in the system causing the longer crank times. Try charging them and see if you're still having the same long start times. Also, the alt. doesn't energize immediately on engine startup. It takes a number of seconds before it starts charging so that it doesn't burn up the glow plugs.

 

The batteries were both new and installed in Feb. Yeah by harder to start I mean it took longer and had to crank more before it started.

 

The last time I had a charging problem was on my 97 Explorer.

A quick look at the charge circuit wiring diagram told me which fuses & fuse links I needed to check.

Sure enough the "Generator/voltage regulator" fuse was blown.

The new fuse did'nt blow, so problem solved.

Before you do anything else make sure this isn't just a simple blown fuse.

 

Checked all the fuses they are good. After getting it started and waiting several minutes the alternator was only reading 12 volts, had the warden rev it up to 2000 rpm and hold, it was then reading 13.5 volts. I am gonna try to charge the batteries then see what happens. It has been running on its own for about 45 min. I am cunfused it doesnt seem to be the alternator or the batteries?

 

It could have been a combination of a high pressure oil leak causing extended cranks with a starter drawing too much current, thus you eventually had to jump start it. If the batteries are fully charged and the truck has been running 5 minutes, with loads off you should be looking at somewhere around 13.5 volts. Less than that, you need an alternator.