if the batterys are charged the truck will start up but not put out the required voltage from the alternator, less then 14v. alternator is new and we checked it twice at the local parts store. all wires have continuity, no voltage drops, new fusible links, all fuses are good, all grounds are good. the battery indictor lamp is on and stays on if the truck is running or not. i think it has something to do with some sort of sensor but im trying to get some advice before i start ripping all the sensors out and stuff. any advise would be greatly apreciated.

2000 ford 7.3 reg. cab long bed xl, no power options, 6 speed

 

It's not a sensor. The batt light is run directly off the alt connector. You may have a bad connector right there at the alt (the three-pin clipped one) -- I just replaced mine.

 

would that bad connector affect the entire charging system?

 

Yes it would even though the alternator it turning it might not being turning on the field.

 

just checked the connector got 1.4v out of one side and the other is a good ground. batterys are currently at 11.3v but the gauge on the dash is reading zero with key on engine off. batterys are currently charging. can the battery light be on for just low voltage? also can the crank position sensor have any affect on the charging system or a new chip? did a VAT test last week and the truck passed when it was running. alldata has nothing for this situation i really just need a good technician to shine some light on this subject.

 

is the batteries at 11.3v while the truck is running? if so that is not charging, you should see around 14v if the alternator is charging. My understanding of it is that battery light will only come of if the alternator is not working. when My alternator was starting to go could watch it flash on and off for a few days erratically why sitting. was able with a buddy to watch it on the Meter jump up and down on voltage. I'm not sure what your suppose to be getting on the connector I can check mine for you in a bit if no one else chimes in.

 

I am busy chasing an electrical gremlin in my truck as well. Not sure yet if the alternator is starting to go, or the batteries, or the first is contributing to the decline of the second.

Where can you check the alternator output? On the posts of the passenger side battery?

 

The light does not come on due to voltage. If it did, it would come on while the GPs are on. The batt V on my truck sits between 12 & 12.5 until the GPs shut off, then it jumps up to 13.5+. It only comes on when it isn't charging, and that is determined by the connector on the top of the alt.

 

Like Izzy said, though mine is a bit different...

Engine off, key on, GPs on, 11v
Engine on, key on, GPs on, 11.5
Engine on, key on, GPs off, 12v+
after idling a bit, typically about 1 minute 13v+
normal running, 13.4 to 14.2v depending on how hard the alternator is working.

With a voltage gauge in my cluster I see this all the time. If you are not getting a charge then just as suggested check the connection on the top of the alternator, make sure it is CLEAN! Take it apart and be sure.
If you are not maintaining 13.4v+ then you are not charging then the alternator needs to be replaced, if you are maintaining 13.4v+ and you still are having a starting problem without putting a charger on the truck then chances are you have one of two problems.

One: You have a bad battery or bad batteries
Two: Something is drawing current off your batteries while the truck sits with the key off. This is not uncommon. There are a couple things that can do this but it can be checked with a volt meter that has a 10amp current meter.

loosen a terminal but do not disconnect, just get it loose so you can pull it. Get the meter ready and put the positive to the positive side and the negative to the negative side then slide the terminal off with the volt mete leads still attached to both the battery and the cable, one lead per.

Hope that makes sense.

I say to do it like that because if something on the truck pulls more than 10 amps you will blow a fuse in your meter and on my truck it sparks when I connect the cables. Probably has something to do with the capacitor I have in the truck for time travel :-P

Seriously though, between my amps and the cap it will spark something fierce.