Is there a "quick & easy " way to test the voltage regulator? Last night I was working on the back up lights and measured 16.5 volts to the input of the switch while the car was running. Measured the voltage at the battery, and it was also 16.5 volts while running. When the front fans turned on, the voltage dropped to 13.3. An I looking at a bad regulator or alternator?




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The battery wasn't dead, the car always starts right up. But I have to admit that the alternator belt squeals for a little while and the amp meter is almost pegged for the first minute or so, but should I ever see the higher charge voltages at other points in the car that should only be at 12 volts?

I had a bad regulator, and all of a sudden my lights got REALLY bright, and my in- the-car volt meter was showing 16.5 VDC.

The plug-in regulators (the solid state ones, with the silver cover) are so cheap ($20, just a guess) that this is a case where you might want to buy one and swap it, and see if it makes a difference.

Get one of the volt gauges that plugs into your cigarette lighter (another $8) to monitor the voltage easily while you are driving.




With the engine running you should measure the voltage being maintained by the regulator anywhere that is supposed to be "hot". With the engine off (key in off position) you should measure the charge the battery is holding across the battery terminals.

The old electro-mechanical regulators were "supposed" to be set at 13.65 volts if my memory is working.  The solid state replacements run closer to 14. And most modern alternators with built-in regulators run even a little higher. I highly recommend replacing any electro-mechanical regulator with a solid state replacement. The charging system operates much better.

If the voltage looks OK at idle, but increases as engine speed increases, that's a regulator problem. If the voltage looks OK, then jumps high, then drops back to normal again suspect a sticky electro-mechanical regulator.

Batteries are usually 2.1 volts per cell (12.6 volts).  However decades ago (80s & 90s) I ran Delco batteries which were closer to 2.2 volts per cell (13.2 volts). A Delco battery that measured 12.6 was undercharged. My point being that 12.6 volts isn't necessarily the sign of a healthy battery in each and every case, it depends on the battery.

Alternator diodes fail sometimes. On some occasions an alternator with a bad diode makes a growling sound that sounds like a bad bearing ... but its not its a diode. If a diode fails open the alternator will have a reduced output. If the diode fails "shorted" the alternator will have AC current in the output. Anything that has computer circuits (engine management, stereo) may display problems if the charging system has an AC component.

CAUTION!!  16.5 at idle is too high. Could me much much higher at higher RPMs if the alternator/regulator is shorted "full field".  . (14.5-14.7v max at any rpm is normal, I have seen 15v max but not crazy about it. )   

Use safety glasses or face mask. Check the water in your battery , if  you can see the top of the lead plates you could have a very dangerous situation -ventilate it well before you do anything (blowing compressed air works, don't use anything electrical)  .  The water should be covering the lead plates but below the plastic lip inside the holes. (Always have plenty of fresh water or water and bakeing soda mix close by to neutralrize the acid )

Overcharging  , due to a stuck or poorly calibrated voltage regulator WILL. Boil your battery water dry and turn your battery into a 40lb lead and plastic bomb or overheat it if it's a gel cell.  Disconnecting the battery may be the only spark needed to ignite it. Ventilate first and top it off with distilled water before you do anything. Maintanance free batteries still need water in them, you may have to work at it to get the caps off or they may be glued closed on some (not much you can do in that case). 

 I have seen batteries blow up first hand a few times. (Pushed a huge outward dent in the hoods of a 70's Volvo and a 68 Plym Satalite. Something you never forget.  I aslo know a guy that had his lip torn off and a face full of acid (almost blinded him). 

Be careful. Better safe than sorry.  



Thanks for the advice. All could be possible, but I'll take a second look at it over the weekend. Starting with the battery alone without the motor running, and inspect all the chassis grounds. I do suspect both the regulator and alternator might be bad. Seeing as I've never replaced them.




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