New alternator test...am I missing something?

[coolwind57]

Got a new battery and just installed a new alternator.  Still no charging at the battery upon start.

 

Here's what I did:

1.  Checked voltage at battery without starting:  12.3v

2.  Checked voltage at alternator post:  11.7v

3.  Unplugged dual-wire connector at bottom of alternator and probed yellow wire with key on ACC:  12v

4.  Plugged connector back in, started engine and probed battery terminals:  12.1v

5.  Checked ground at engine (2-year old cable in excellent condition):  Tight and dry

6.  I have an additional ground I installed from the NEG terminal to the frame and it is fine too.

7.  With engine running, probed at solenoid (I'm assuming that's a solenoid where the fat red alternator wire terminates on the inner fender):  12.1v.

 

Besides running the truck up to Autozone for an alternator load test, am I missing something?  New, not remanufactured AC Delco 100amp alternator, so It would be unlikely to be bad from the factory.  Why wouldn't I be getting my 13-14v at engine idle?

 

 

 

 

[coolwind57]

Got it figured out.  It works, but I still don't understand why it's working.

 

Found a 7.5v instrument fuse was blown.  Replaced it and now I'm getting 13.7v to the battery at engine run.  I had pulled the manual and looked at the wiring diagram.  Why a blown 7.5v brown fuse that goes into your fuse block that works your instruments would prevent the alternator from charging is beyond me.  I've studied that wiring diagram and can't seem to solve why just replacing the bad fuse works.  Looks to me like it should only effect the gauges (idiot lights) only.  I give up and will just drive my damn truck now.

 

Earlier, I had noticed that my battery indicator idiot light was not coming on at engine starting.  That caught my attention.  Anyhow, I popped a new fuse in there and started the engine.  During engine start sequence, the idiot light came on and went off as it was designed.  I immediately notice the engine had an very slight, extra, barely-noticeable noise as it was idling.  It was the alternator working its magic, firing juice back to the battery.   Multi-metered to conform the hungry battery was being fed once again. 

 

Thank you Jesus.  Hope this ordeal helps someone one day.    

[acfortier]

The battery indicator light is part of the alternator circuit, so I guess it's not too puzzling that with a blown fuse it wouldn't charge? Seems odd to me, too, but I guess it kinda makes sense? 

[coolwind57]

4 hours ago, acfortier said:

The battery indicator light is part of the alternator circuit, so I guess it's not too puzzling that with a blown fuse it wouldn't charge? Seems odd to me, too, but I guess it kinda makes sense? 

Have a look at the schematic...next time you're really bored.   Reading schematics is certainly not a stength for me, but I looked over it for several minutes before giving up in figuring how a blown 7.5amp mini fuse that's listed for "instruments" would knock out the entire charging system of the vehicle.  Renix had some goofy things going on, especially with lack of good grounding throughout.  My 89 didn't even have a relay for the headlamps either--full voltage going all the way up to the headlight switch.  I would had figured all vehicles would had thought to use relays for headlamps by 1989.  

 

Love me truck, but it keeps me on my toes.