Question about 1990 GMC Suburban

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I have a1990 chevy surburban it has new battery ,new alternator,new terminals,but is not regulating the alternator to battery what could it be

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Check the cable coming from the back of the alternater going to the battery make sure it has current flowing throw it if not replace it

Posted on Jan 23, 2013


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Gas is expensive, I know. Try at least buying one gallon though, it'll work wonders. But seriously, check to see if your plugs are fouled, if your catalytic convertor is clogged, or if you have a faulty fuel pump/bad fuel filter. Also check amperage on your alternator, because if it's shot, you're running on straight battery power which doesn't last long.

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I assume a new regulator has pased QC and is OK. Is your volt meter accurate? Just a tip - we do not test alternator by removing terminal. That burns the alternator.

Are you getting the 12.1 v from alternator at alternator end or at the battery terminal? Check the connection between the + terminal on alternator and the battery. That wire might be disconnected at the starter motor.

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Put a volt meter across the battery terminals and check the output. You should be seeing around 13.5 volts at idle, no higher than 14. At idle with all accessories on, it should read just a bit lower but should not drop even after ten or so minutes. Your alternator has a built in regulator so when you get a new one, that's all you need. Also make sure the heavy red wire from the back of the alternator is secure at both the alternator and the battery (the extra small wire on the positive terminal) Any problems, ask me and I'll give you more if needed!!! Careful when checking the back lead on the's always hot when the battery is connected.

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There is a ground some were that is causeing the battery not to charge put new selinoid ,new battery,alternater,new key lock cylender check wirers fuses relay switches and battery still wont charge

It sounds like you have done a whole lot of replacing and not much "diagnosing". Did you chech for battery voltage at the alternator? There should be battey voltage at the large Black/Orange wire that is on the B+ terminal of the alternator. This wire should have voltage all the time. If there is no battery voltage, you most likely have a burned fusible link at the starter relay area.
There should also be voltage at the "S" terminal with the ignition on. If there is no voltage, then check for voltage at the "S" terminal of the voltage regulator. If there is no voltage at the "S" terminal on the voltage regulator then check the "I" terminal on the regulator for voltage.

NOTE: The voltage on the "S" terminal should be 1/2 that of the voltage on the "I" terminal.

If there is voltage on the "I" terminal, make sure your voltage regulator is grounded properly to the fender and retest to see if it is charging the battery. If it is still not charging, disconnect the regulator connector and connect a jumper between the "A" and "F" terminals of the connector. Start the engine. The alternator should now be charging the battery at high voltage (usually over 15 volts) If it does, replace your voltage regulator. If it does not, then you need to check your wiring between the voltage regulator and the alternator.

Please also review this article:

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Here is a easy way to do it have a voltage tester on hand///multi meter put the positive to positive and negative to negative you should have engine running your voltage reading should be 12.79 up to 14.29 anything under bad alternator anything over 14.29 is bad that's over charge that usually cooks the battery.And truck not runnig test the battery same fashion your reading should be 12.79 up to 13.29 is good under battery no good.Good luck to you

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Check the red wire from the alternator where it hooks into the battery terminal. The wire may be corroded inside the plastic insulation of the wire and not making connection. It may even look ok and still be a bad connection.

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