Low voltage...

[79K10Crusher]

My truck would not turn over one day..installed a brand new interstate battery.  Cranked right up.  Drove it down the road and parked,it back in garage.  Next day...barely enough to turn engine over...charged battery...cranked up but voltage was barely above 8 on guage.  I drove it about two miles down the road and back home.  Cut it off and it would not start back up.  Checked voltage at alt and it was not charging battery.  Only 11.6 volts.  New alt and battery...still doing the same thing..i checked the connections for the plug at alt and terminal on the back...they were good..what else could be draining my battery?

[79K10Crusher]

Started is engaging and solenoid are ok...something is draining the battery

[bake74]

     You need to find out why when running the alternator is not charging.  Your other issue sounds like a short somewhere in the wiring in the circuits that have 12V constant power.
    I had a Blazer that was doing the same thing, found a short in the wire loom in the engine bay, it would drain my battery every other day.

[79K10Crusher]

When I jump start the truck...checking the battery..there is still only 11.6 volts. 

[bake74]

When I jump start the truck...checking the battery..there is still only 11.6 volts.

     Your alternator should be putting out at least 13.8 to 14.2 V (ideally)  when running (your rpm is not too low on your truck is it ?  This could be a problem for the alternator) at the battery cables. 
     Start the truck, remove the negative battery cable, retest the ends (with the negative not touching anything), the alternator should be producing the voltage I stated and your truck should keep running with out a battery hooked up.
     If you are reading over 15 V, there is something wrong with your alternator. 
 Also check the belt and make sure it is tight and not slipping.

[bake74]

     You could always raise the RPM a little also to see if your alternator starts putting out the right voltage.

[79K10Crusher]

My truck is set a little high at idle..decent size cam....

[bake74]

My truck is set a little high at idle..decent size cam....

    Then you should not have a problem with low idle.

[79K10Crusher]

Belt may be running a lil loose..  I did hear it squeal but it's turning the alt......?

[hatzie]

The alternator is either bad or charge is not being requested.  Leave the low amp field plug inserted and test at the plug with a meter.

Terminal #1 is the exciter circuit that either runs through a GEN ALT bulb or through a resistance wire to the ignition +12v. When you turn the key on it energizes (+12v) the fuse block (ign) side of the warning lamp and the alternator side of that lamp serves as a ground when it's not generating power.  Without a resistance from a bulb or resistance wire it would be a dead short.
Hooking your meter from terminal # 1 (exciter) to ground should read 0v with ignition off, 0v with the ignition on, and 14.5v with the engine running.  If you don't have any volts with the engine running you have a problem with the voltage regulator inside the alternator.

Term #2 (remote sense) runs to a fusible link at either the bulkhead stud on the firewall or the BATT stud on the starter.   
Hooking your meter from Terminal # 2 (remote sense) to ground should read battery voltage with the ignition switched on or off.

http://www.pirate4x4.com/tech/billavista/Wiring/Part2/#siseries

[bd]

Belt may be running a lil loose..  I did hear it squeal but it's turning the alt......?

Checking alternator belt tension:
With engine off, firmly grab the alternator fan with your hand and try to rotate it.  If you can rotate the alternator fan at all with your hand, the belt is loose and needs to be adjusted.  This method works for all belt driven automotive and truck alternators through Class 8 trucks, regardless of make.

[79K10Crusher]

Good news...I charged my battery today with new alt and it was topped off at 12.7 volts.  Drove it 30 minutes and came back home.  Cut it off and let it sit a while.  It started right back up.  I think that the alt quit charging causing the battery to drain.  I then put a new alt on a dead battery...which it couldn't charge....but after charging the batt..all is well.  Sad days when our old square body's aren't running the streets...

[bake74]

     Glad you got it figured out.

[79K10Crusher]

As my luck would have it...it has started back.  I found the fuseable link wire melted in two.  I replaced it with another piece of wire and the alt immediately started charging the battery.  Bad news...it started burning the wire up in about 5 seconds.....any ideas?

[bake74]

As my luck would have it...it has started back.  I found the fuseable link wire melted in two.  I replaced it with another piece of wire and the alt immediately started charging the battery.  Bad news...it started burning the wire up in about 5 seconds.....any ideas?

     I still think you might have a direct short.  Did you replace the fuse able link with a fuse able link or just a wire ?  It needs to be a fuse able link.  See how to fix a fuse able link in the tech section.