everything is new, but still won't charge...

[Bayareajim]

Ugh, old thread, same problem. And I'm a commercial electrician - this thing has me stumped. Yeah, I'm a newbie-ish, but been lurking, reading and learning for years.

1972 GMC K2500 4x4, 350 engine, externally regulated. Voltage guage, not light.

Simply converting to internally regulated may do nothing, I want to fix this problem then convert later.

New everything, battery (x2) regulator (x2) alternator (x1)

12.4volts best I can get. Battery won't charge. But never has never died while engine runs, telling me the alternator is working, lights are bright, fan motor etc all on - just no juice to the battery.

This seems to be a common problem with these trucks. Rewire with new oem engine compartment harness? 2 days in troubleshooting, I need a beer.

[VetteVet]

Welcome to the forum.
The first step on this problem is to check for 12 volts on the brown wire on the regulator plug.
Key on---12 volts.
key off---0 volts.

So the same at the alternator plug only the white wire will be 12 volts with the key on and zero with it off. The white wire is an extension of the brown wire on the regulator plug.

The blue wire should show 12 volts key on or off. The engine does not need to be running for any of this test. If these two wires are reversed in the alternator plug it will create a voltage draw and drain the battery.

Check for 14.5 at the large red wire on the back of the alternator with the engine running . If you read battery voltage then the alternator is not charging. The battery will sustain the engine and lights and fan for quite a while by itself.

[Redneck Rydes]

Get rid of the external regulator ,nothing but problems with that set up

[RichardJ]

What makes you think you have the same problem as 71wongbed who started this thread in 2009 or the problem Billhillys had in 2016?

Your post follows my last from two years ago in which I complained about resurrecting old posts and here we are again.
The only similarity I see is a troubleshooting technique that involves throwing parts at some problem.

>>12.4volts best I can get.<< Meaning what?

>>has never died while engine runs,<< I've driven 80 miles with a bad alternator and a good battery.

>>350 engine, externally regulated. Voltage gauge, not light<< Aftermarket Voltage gauge? Original gauge is an Ammeter.

Please, do not refer to wires by insulation COLOR. Refer to wire by usage or terminal points.
As an electrician, you may be used to painting or taping insulation to denote usage. Standards for automotive insulation color should be considered out the window. In 50 year old vehicles if someone didn't change a wire to a different color, the manufacture may have.

The 10DN, 37 Amp, externally regulated Alt puts out very little current at low rpm. Check battery voltage at 1500 - 2000 engine rpm.

Do not, under any circumstance, remove battery cables from battery while engine is running. It will not provide you with any troubleshooting information and could damage the alternator diodes. Do not listen to anyone that tells you to remove battery cable.

[harpo231]