Alternator warning light stays on

[yarbe]

I have a '70 pu with a 302 engine. The alternator warning light stays on even though the alternator is charging the battery just fine. The alternator is putting out 14.5 volts and the battery always stays charged with at least 12.5 volts. The battery is one year old, the alternator is 6 months old and the voltage regulator is 2 months old. The problem did not develope with any of these replacements. It appeared about 2 weeks after the regulator was replaced. I suspect a problem with the new regulator or a ground problem but don't know to troubleshoot. I have some specific questions. I assume the light comes when
wire #904 is at ground. If true, does this take place within the regulator or is there a relay involved? If it's a ground problem where should I look? The battery ground wire is new and I believe the regulaor base is well grounded. I have not replaced the #26 wire from alternator to ground. Thanks.

[Thunderfoot]

I have some specific questions. I assume the light comes when
wire #904 is at ground. If true, does this take place within the regulator or is there a relay involved?

You are correct and it is just the Voltage Regulator!
The Regulator has circuitry that grounds this 904 wire. The way it's supposed to work it that it grounds until the alternator starts charging then it applies voltage to this line after the alternator starts charging.
You might unplug the voltage regulator to see if the light goes out, if it does then it is the voltage regulator causing the problem. If it doesn't go out, then check that 904 wire back to the cab / instrument panel / ignition switch looking for somewhere it may have shorted to ground.

And to the site!

[yarbe]

Thanks Thunderfoot. I replaced the almost new voltage regulator and that took care of the probem.

[Thunderfoot]

Thanks for the update
There have been lots of people having problems with new Alternators and Voltage Regulators lately...

[fordman]

made in china