Gauge showing low output alt only 1yr old wondering if it could be regulator or batt or wiring

Could be any of the three, start with getting your battery charged, possibly be bad wiring. Doubtful the alt is bad.

There is a fuse or fuseable link between the alt and battery, and the alt gets a signal from the key to activate the voltage regulator.
I would check for batt voltage at the alternator and you may need a wiring diagram to check for key voltage.

u need to chek for batt volts at the pos pole on the bak of alt.should b batt voltage if not then wire from pos pole on back of alternator to battery could be broken,causing no output tobattery. wiggl voltage regulator wires while engine runs an check volts with a voltmeter to see if it jumps to over 13v wen wiggling connector.also chek fuses an fusible links for continuity.

It sounds like you have a charging problem-alternator is not recharging batt when drive, batt will only go so far before it runs out then you get your symtoms. you would need a volt meter to double check this. Fully charged batt will be about 12.7volts once car is started and running you should see about 13.8 to 14.2 volts at batt terminals if alt. is chariging batt. the other item that can cause this is the volatge regulator that controls alt. which are sometimes built-in alternator and sometimes they are external to alternator. and of course make sure your belt is turning alternator to allow it to work. One other small note if you do the engine running test-somtimes- if your car idles low(600 or 700 rpm) you need to give a little throttle (1000-1200rpm) to make sure alternator is turning fast enough for output test.

Do you have an alternator with 2 field connections and one power output connection and a separate regulator?
If you do,with the engine running,remove the connection from the regulator and jump across the 2 connections in the wire harness,this will give you full field and the alt should show a charge,use a voltmeter on the battery and watch for an increase in voltage.If voltage increases,the regulator is bad or the reg ground is bad.(try cleaning the mounting bolt areas before replacing it)If no increase in voltage,remove the 2 field connections from the alt and ground one and apply battery voltage to the other with the engine running.You should see an increase in voltage if the alt is good.I am assuming you have battery voltage at the alt power output connection at all times?

The "Batt" wire probably goes to the starter solenoid or starter relay. The wire is most likely corroded off or it's making a poor connection. Some vehicle route the power directly to the battery, look for a fuseable link in the wire. Use a test light too see if you have power on both sides of the fuseable link. There should be power at the "Batt" terminal of the Alt at all times, if not start tracing the wire back to the battery. The voltage regulator is built into the Alt. Hopefully this helps.

If you disconnect the battery for 20 min it should kill all memory and reset everything.If not you charge is still low charge up your batt. with a charger.and test your alt. output 13.9-13.7 you have to check the book.I'm not to sure on that.You might have a voltage regulator problem bad batt. Or somthing is hooked up wrong. Mabey the old alt was fine. Have the batt. tested. All alt. well most are rebuilts so you might have a bad one it happens.Make sure that it's putting out a charge.
Loose alternator drive belt or loose or corroded battery cables. The battery itself may also be bad.

I am assuming you are now using a 1976 style GM alt.
The most common and popular model.
You need one 10 gauge wire from the battery to the alternator output.
This can be run directly from the battery +.
Run a short 10 gauge wire from alt output to large wire at regulator plug on alt.
Run small wire on alt reg plug to Bat light wire.
A new alt regulator plug pigtail can be bought at any parts store and is recommended.

The existing regulator should have the connections marked.
One of those wires will be the bat light wire if needed.
If you have a amp meter or voltmeter in the vehicle.....use your existing large output wire (usually red) to hook up to the new alt output connection.

1978????? my best guess would be loose connection somewhere or glazing on a terminal. however with that many years on it I have seen the wires between the alt and batt and volt regulator get rusted under the coating (usually toward the ends) so you could peel back the casing and check that. you may need to replace those wire harnesses

14.6 means your voltage regulator or diode is suspect Despite having new alternator .Ive cross refrenced your smptoms in the haynes workshop manual and alternator is your only end answer.The haynes test is to start vehicle with multi meter connected across the battery terminals,increase the engine speed until the reading remains steady should be approximately 12 to 13v and no more than 14v.switch on as many accessories as possible(headlights heater blower radio etc)check that the alternator maintains the regulated voltage at around 13 to 14v.If the regulated voltage is not as stated then alternator is to be repaired/replaced.Good luck with it and a happy new year.