Alternator good but not charging battery

Discussion in 'Audio + Electronics' started by sethel, Jan 27, 2020.

  1. sethel

    sethel Newbie

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    I installed a remote start module in the truck. Everything works but the alternator is not charging the battery yet was just tested as good. the "dummy" battery light does not come on at any point including keys in on position with the car not running.

    This leads me to believe the brown single wire to the alternator telling it to "energize" and also connected to (via the basic universal Haynes wiring diagram for the full spectrum of gmt400 trucks) the battery dummy light is not receiving signal when the ignition is in the on position.

    Seems to me in the wiring diagram if the battery light doesn't have power then the brown wire from that to the alternator does not have power and the alternator is not being told to energize. I switched the battery bulb with a light I know works in the dash. the working light continues to work and the battery light does not.

    Are you supposed to see the battery indicator before cranking? If so do I just need to somehow chase the brown wire that is behind the dash plugging into the back of the instrument panel?
     
  2. someotherguy

    someotherguy I'm Awesome

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    Yes, you should see the battery light come in during the key-on bulb test.

    Try wiggling the harness connector at the alternator; these get loose/oxidized and can cause problems.

    Richard
     
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  3. Kran

    Kran Newbie

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    you can also hook the wire up to a fuse that has power when the key is on. that will work as well. as a backup solution.
     
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  4. sethel

    sethel Newbie

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    First off thanks guys.

    I cleaned and applied dielectric grease to the connection and got nothing. Wiggled the plug got nothing.

    I spliced the brown wire with a quick disconnect. After starting the truck I connected it to the auxiliary post in the fuse box. And I got 15 volts at the battery. Backup Success.

    that’s a hot all the time post but I’ll find a ignition fused source if I need to use it for longer.

    Really want to track my original wire back to the gages but that is proving remarkably difficult.

    i just don’t get if my bulb is good in the instrument panel where could this disconnect possibly be??

    here’s the wiring diagrams showing the 1 brown wire I spliced into simply going to the dash lights.

    13EDFD5F-A411-4321-9DF6-08AB733AD8E5.jpeg

    CC7CF55E-5D4D-4759-A2DF-1C18536972CA.jpeg

    920BAC0F-4561-4274-87E4-836F82C57C6B.jpeg
     
  5. Kran

    Kran Newbie

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    i wouldnt keep the alt turn-on wire on a hot wire. it will keep the alt on and drain the battery.
     
  6. sethel

    sethel Newbie

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    Yea that’s just where I tested it. I’ll find a ignition on circuit if I need to use it.

    right now I’ve tracked continuity in the brown wire with my multimeter through the engine bay. This picture is the fire wall bus. The pin that the tip of the lead from my multimeter is pointing at is the brown alternator wire. Just in case anyone in the future pulls this thread up with this same issue.

    the Fire wall bus came out with a T30 bit and just pull the rest of the way. Also note the top of the picture is the bottom of the bus when installed. and left is passenger side Right is driver side of the bus from the engine bay.

    I’m good through here. Going to reinstall. Not sure where the discontinuity is yet.

    A458C134-8D00-4C74-BE00-568AFB09C0E1.jpeg
     
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  7. Redneckgeriatric

    Redneckgeriatric I'm Awesome

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    it appears there is a diode at the pink wire/ bulb connection.
     
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  8. Jglew82

    Jglew82 I fix stuff

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    Did all this start happening after your remote start install? If so, I'd go back over all that wiring and see if something is incorrect. The exciter circuit is a pretty simple one, so it shouldn't be too hard to locate the issue. Have you checked continuity between your firewall connection and the cluster harness connector?
     
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  9. sethel

    sethel Newbie

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    yea it worked up until that install. But I also went through the process of removing the entire dash to fix the infamous blender flap doors that fell off in my rig. So everything was disconnected. And my truck was sitting for quite some time like that.

    But my remote start/alarm system was my first thought of the culprit. But looking at the wiring diagram the pink wire feeds a slew of lights and gages in the dash. That pink ignition is the only wire in this circuit I spliced into for that install. And since all other lights and gages were working it became evident that my ignition power was distributing fine.

    I tested for continuity through the circuit. And got nothing. The fire wall bus above was the first time I found continuity. I put some dielectric grease on the connection there. As well as removing the gage terminal assembly. I was so happy to know that it all snapped out of the dash. I was real concerned I wasn’t going to see the brown wire there without removing the dash. Cause I ran new sub and amp wires right by this assembly and thought the brown wire may have became disconnected. It wasn’t. Put some dielectric grease there too.

    you can see in the photo that the brown turn on wire is the 3rd terminal from the left on the top of the assembly. I ran a wire from the plug at the alternator terminal and tested continuity to this pin in the dash. SUCCESS!

    Not sure why only that pin at one of those points was having issues and not others. But next time around anything I disconnect will get a little more love with dielectric grease before I reinstall.

    thank you all for chipping in while I figure this problem out.

    64CE94B3-E9CC-4A3F-8522-A05B469C093E.jpeg
     
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  10. Jglew82

    Jglew82 I fix stuff

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    Good find, and great explanation. Glad you got it sorted out!
     
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