To onefarmer and cOOnhunterjoe. Here's what I got. I bought a meter and tested the following wires. With the truck off and the key off I tested the battery's and got 10.82 volts, with the black on the battery and the red on the large post on the back of the alternator I got 10.58 volts. The 3 wire connector on the top of the alternator the left side wire was a yellow wire and it read 10.58, the middle wire which is the jumper wire back to the alternator read .05 volts and the right side wire which is green read 2.44 volts. I started the truck and was going to do the rest of the test and the truck died and will not start. The batterys seem to be dead again and they are new battery's. I removed the battery's to charge them and I tested them by themselves and they both read 10.25 volts. They are on the charger now. Did I do this right. Remember I have a 1997 f-350 ford dually with a 7.3 diesel

 

i think i remember the truck, this is the one that has a new alternator that still wont charge?

you need to test the 3 wire connector with it unplugged from the alternator first. with it unplugged the first wire shuold read battery voltage as you said it does already, just double check it. the other outer wire should have 0 volts with the key off, then turn the key on and you should have battery voltage, check that first and get back to me.

 

x2 on that

I'm concerned about the 10.8v at the battery. It should read a bit over 12v. Maybe the batt was already run down or the meter is off that much. Double check the meter by testing another vehicle.

 

Help, I was reading this post and this is similiar to my problem. I have put in new batteries and a new alternator and my truck still reads on the N on the Volt gauge. I checked output on the when running and it is putting out just over 12 Volts (the same as the alternator I replaced) I did the test you mentioned with with positive results. The funny thing is when you drive the truck for awhile (15minutes or more) the needle on the gauge returns to where it should be. Unfortunately at those times I have not been where I could do Voltage tests. Turn the truck off and we are back where we started. Any Ideas?
Thanks screech.owl

 

Sounds like a bad voltage regulator to me. That'd keep it from charging. Especially w/ new batteries, they arent usually that expensive like $12, might want to take that of and get it chk'd most parts stores can do that for free.

 

coonhunter what would be the cause of the problem if the were no power to the alt with ignition on?pcm?