 No Alt. light after start up but battery not topping off .. |
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| Literati914 |
 Aug 9 2025, 10:35 AM
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Advanced Member  Group: Members Posts: 2,086 Joined: 16-November 06 From: Dallas, TX Member No.: 7,222 Region Association: Southwest Region  |
My battery was bought last month.. Alternator light comes on with the key on, but goes out at start up. Battery keeps running low and eventually won't start the car. Does this point to anything usual - VR maybe?
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| Literati914 |
Aug 11 2025, 02:32 PM
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Advanced Member Group: Members Posts: 2,086 Joined: 16-November 06 From: Dallas, TX Member No.: 7,222 Region Association: Southwest Region |
QUOTE(Spoke @ Aug 11 2025, 06:30 AM)  .. If you unplugged the alternator please plug it back in to test. The test I suggested is done with the plug connected as normal. idleing: D+/Red = 13.6v DF/Green = 4.05 etc D-/Brown = 0.05 etc |
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| Spoke |
Aug 11 2025, 04:02 PM
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#3
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Jerry Group: Members Posts: 7,231 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None 
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QUOTE(Literati914 @ Aug 11 2025, 04:32 PM) QUOTE(Spoke @ Aug 11 2025, 06:30 AM) .. If you unplugged the alternator please plug it back in to test. The test I suggested is done with the plug connected as normal. idleing: D+/Red = 13.6v DF/Green = 4.05 etc D-/Brown = 0.05 etc Those are excellent numbers. The VR is working perfectly. The VR senses the voltage at D+ and adjusts DF to output 13.6V +/- 0.4V. I made up that tolerance but the bottom line is 13.5-14V is perfect. I should have asked to also measure the battery voltage at the time of measurement. It runs open loop from the alternator diodes driving D+. If diodes are all good VBAT should equal D+. What is the battery voltage at idle? Positive terminal to chassis ground. What is the battery voltage from positive POST to the negative POST? Just want to see if the battery wires or connections are suspect. Post to Post or Pos Terminal to chassis should be identical if the wires/connectors are good. |
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Posts in this topic
Literati914 No Alt. light after start up but battery not topping off .. Aug 9 2025, 10:35 AM
GregAmy Does this point to anything usual - VR maybe?
What... Aug 9 2025, 10:44 AM fixer34 Could be several things but VR is a likely suspect... Aug 9 2025, 11:24 AM TheCabinetmaker Check the belt tension Aug 9 2025, 12:04 PM Literati914
Does this point to anything usual - VR maybe?
Wha... Aug 10 2025, 07:14 PM
GregAmy
update - the bulb is not blown. I can get it to l... Aug 10 2025, 08:13 PM
Lockwodo
[quote name='GregAmy' post='3218602' date='Aug 9 ... Aug 10 2025, 09:41 PM dtmehall I experienced similar symptoms about 4 years ago.
... Aug 10 2025, 07:24 PM Spoke There is a quick test you can do on the alternator... Aug 10 2025, 07:26 PM Literati914 just noticed that my alt bulb has blown after tigh... Aug 10 2025, 07:26 PM Literati914 update - the bulb is not blown. I can get it to li... Aug 10 2025, 07:42 PM Literati914 Alt light with ground provided by test light… li... Aug 10 2025, 07:54 PM Literati914 You can see the rat’s nest of wires here Aug 10 2025, 07:55 PM Literati914
update - the bulb is not blown. I can get it to ... Aug 10 2025, 08:39 PM Literati914
[quote name='Literati914' post='3218779' date='A... Aug 10 2025, 09:17 PM Spoke
removing the alt plug at the relay board in order... Aug 11 2025, 05:30 AM Literati914
If the battery voltage, measured at the terminals... Aug 11 2025, 01:35 PM Lockwodo
If the battery voltage, measured at the terminal... Aug 12 2025, 12:04 PM Literati914
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What is the battery voltage at idle? Positive ... Aug 11 2025, 04:27 PM Spoke
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What is the battery voltage at idle? Positive... Aug 11 2025, 06:41 PM Literati914 I did the test - jumper wire between D+/DF (with V... Aug 11 2025, 07:06 PM Literati914
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Can you measure the battery voltage and D+ wi... Aug 11 2025, 07:15 PM Spoke
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Can you measure the battery voltage and D+ w... Aug 11 2025, 11:34 PM GregAmy I tend to agree that it's a diode, which is a ... Aug 12 2025, 07:50 AM Superhawk996 I’ve been reluctant to chime in . . . . Cause Iâ... Aug 12 2025, 09:14 AM GregAmy ^^^ Good points. Aug 12 2025, 09:58 AM Literati914 Still dealing with the problem of alternator not c... Aug 27 2025, 04:17 PM emerygt350 I have really enjoyed my negative terminal to the ... Aug 27 2025, 04:59 PM Literati914 I've already installed something similar - top... Aug 27 2025, 05:18 PM Literati914 Also, I just found the following break in the wire... Aug 27 2025, 06:36 PM Superhawk996
Also, I just found the following break in the wir... Aug 28 2025, 11:38 AM emerygt350 Might be, however I wouldn't rely on the 50 ye... Aug 27 2025, 07:50 PM VaccaRabite It does not take much of a voltage drop to dischar... Aug 28 2025, 10:02 AM Literati914 OK then, the plan is to run a wire off the lower p... Aug 28 2025, 10:24 AM KELTY360 Beware adding two fixes at once. The added ground ... Aug 28 2025, 11:02 AM Literati914
If you want to measure the voltage drop in that c... Aug 29 2025, 11:50 AM Superhawk996
Probably normal :confused: but would that be an... Aug 29 2025, 07:30 PM Literati914
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If there is any doubt in your mind about paras... Aug 29 2025, 08:50 PM |
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