Need help with charging system

[TheGTkid]

So here it goes guys
4.0 ranger with a 5spd 1996
The charging system is failing
1.5v off the alternator post
12.5v off the positive battery terminal
Disconnect negative post while the truck is running and she shuts down
When the battery dies the truck shuts down
Brand new alternator, tested good at both AZ and Oreillys
Brand new belt tensioner keeping great pressure on the belt
All fuses are good
And connecting pins are in great shape
Help!
Any ideas at all?
Further info;
I replaced alternator fuse about 5 times in the last 6 months

 

[koda2000]

have you checked the mega-fuse on the back of the power distribution box? also try jumping it. is your BATT/CHARGE light in the instrument cluster working during the bulb check? if not, the battery will not charge.

 

[Robman]

Check your connections.

 

[jremington59]

When it's running what do you get for voltage at the cable ends.

 

[Robman]

well, alternator should be putting out 14 volts or so.

 

[SoNic67]

If you have 12.5V on battery and 1.5V on alternator post, then surely the connection between the two is broken. Mega Fuse is a good starting point.

 

[koda2000]

If you have 12.5V on battery and 1.5V on alternator post, then surely the connection between the two is broken. Mega Fuse is a good starting point.

the odd thing is that that battery is nearly fully charged. 12.6 volts, or higher, is 100% charged. how can that be if basically zero volts at the alternator? poster has answered no questions, so no one can't help him. maybe he's figured out he was touching the wrong post on the alt.

 

[SoNic67]

Well, sounds like he did used a new battery (pre-charged) or he did charge it with a plug-in charger.
It will last for a day without having the lights on.

 

[TheGTkid]

I hope you guys can excuse my absense!
I work thirds so im either working sleeping or eating!
The dashlight is on, thr truck is running
12.5/12.8v from battery
Disconnect battery ground/black while running it shuts down
Connect, fires up
The alt, 1.5v when disconnected
Connect battery, same reading as the battery
Full charge batterylasts about 6 hours
Im going through wiring inspection now
Does anyone have any clue as to where i can get fusible links?
Or coded wires?
Any other thiughts guys?

 

[TheGTkid]

If you have 12.5V on battery and 1.5V on alternator post, then surely the connection between the two is broken. Mega Fuse is a good starting point.

Off-hand do you have any idea which fuse is the mega fuse for the alt circuit?

 

[koda2000]

well, you alternator is definitely not charging. the fact the that dash light is on means that the alternator should be getting turned on when the engine is started. the fact that you show no voltage at the "B" (large) terminal on the alternator eliminates wires/fuses after the alternator, so (assuming the alternator did test good) your problem has to be in the wiring going TO the alt. do you have a wiring diagram? if you don't i can tell you where to get one free. you can buy fuseable link wire at Autozone (looks like brown piece of wire).

free wiring diagrams:
lYou can find one at http://search.ebscohost.com/. Use RRCC and rebsco when signing in.

 

[Turdle]

Check that there fuse 17 under the hood-

Does this box match yours? I just pulled it off google-

 

[SoNic67]

Off-hand do you have any idea which fuse is the mega fuse for the alt circuit?

Follow the big/thick cable from alternator towards battery (+) terminal. Somewhere you will find the plastic box that has the fuse, usually is attached to the fuse block, protected by a plastic cover.
Google search with pics.

 

[koda2000]

Follow the big/thick cable from alternator towards battery (+) terminal. Somewhere you will find the plastic box that has the fuse, usually is attached to the fuse block, protected by a plastic cover.

if there's no voltage at the "B" terminal of the alternator, there's no power being produced or flowing to the mega-fuse. the alternator is not getting switched on.

 

[SoNic67]

Well, he said he checked the fuse that feeds the alternator regulator. Which one it is - Owner Manual.
Agree, that would be the first one to check...

 

[koda2000]

Well, he said he checked the fuse that feeds the alternator regulator. Which one it is - Owner Manual.
Agree, that would be the first one to check...

#17 in the power dist box i guess.

 

[BustedKnuckles24]

I just finished chasing a similar problem in my Toyota Supra. The #17 fuse protects the circuit that should provide reference voltage to the alternator's voltage regulator. This circuit is required for the alternator to produce voltage, because this powers the field coils in the alternator. Pull the voltage regulator connector off the alternator and see if you get battery voltage with the key on, engine not running. If you cannot find the reference voltage, there is your problem. Secondly, ohm out the wire from the battery post of the alternator to the battery. There should be very little to no ohms resistance. High resistance or open circuit is also a problem.

 

[TheGTkid]

My trusty back yard mechanic is not liking the power wire to the starter... Gonna crawl under there and take care of that tonight. I agree that the alt isnt being told to turn on, so i guess i have to figure out that communication from the computer to the alt (shouldnt that be a logical solution?) i am near the poibt of rewiring the whole damn charging system
Thank you guys for the ideas
Ill check the fuses once more, and get my electrician dad to help me look on the ohm readings