BTW, running at idle with the new battery gives about 13.8 volts - totally normal.
Have you checked the fuses and the relays?
Probably bad voltage regulator....
Most regulators are built into the alternator, even in 94. Know that’s the case for Hondas and Toyotas of the same age.
Are you sure the regulator isn’t built into the alternator?
Sounds like a bad voltage regulator.
It’s your alternator which has an internal regulator....if it is the original equipment....it’s almost 20 years old
Time for a new one....
Thankfully it’s a Nissan, if it was a Chevy, you already be on your second or third replacement...
Have you tried turning it off and rebooting it?
It behaves as if the alternator was functioning backwards.
You could have high resistance caused by corrosion in one of the battery cables or terminals. This can cause the regulator to crank out too much voltage and light the lamp.
It could also be caused by a bad or weak diode in the Alternator. Any good parts store can check the Alternator and tell you what if anything is at fault.
Very likely, it’s a Windows 8 problem. Always is.
Either that, or it’s Bush’s fault.
If you can get the alternator out, most part stores will test it for free.
Have you checked the blinker fluid?
It’s the voltage regulator and it is almost certainly part of the alternator. Best option is to replace the alternator. I once had a weird problem where my rebuilt alternator would shut-off when it got hot. So if I took it to get a warranty replacement, they would test it, and it would look fine (since it wouldn’t be hot). Drive it for 15 minutes, it cuts out - but they can’t do that on a test stand. So, I figured the best option was to hard-fail it. So I plugged in 120V to the voltage regulator terminals (the smaller wires) for a couple of seconds and nothing happened. Then I ran the alternator on the car and the voltage immediately zoomed up to 16V (just like you)...I had popped the voltage regulator electronics and it no longer regulated. At that point, I took to to the auto store and got my warranty replacement.
In your case, you’re killing your battery with such a high voltage, and also stressing all the electronics in the vehicle - get the new alternator and be done with it.
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The circuit that controls the Indicator light is Usually part of the built in Voltage regulator. And it may be that this function is triggered by Conditions other than just under charging. If you are really at 16 volts then it sounds like you are overcharging. You really should replace the Alternator. Don’t buy the cheapest brand sold at the auto store or you may be sorry as they often have a high fail rate. I have had good luck with Duralast from Autozone.
Not suggesting it’s related or a problem, but since you don’t mention it, it’s a fair assumption it needs stated:
I once was in an auto parts store fetching bolts and a guy with a Jeep was having some issues. While I was there, the staff swapped out 3 different batteries...NONE would kick over his starter. They then blamed the starter and were looking it up to price it. I pulled him aside and asked him if he wanted to save some cash and trouble, as I heard/saw what the Jeep was doing when the last 2 batteries were clamped down and he turned the key. He said ‘yes’. I popped off each cable from the battery scored the inside of the clamp with my key, pressed it on hand tight and had him turn the key: Started right up. Bottom line: Corrosion is a dielectric (insulator). That goes for lead terminals, Weatherpack connectors and grounds.
What I’m getting at is you have a 20 year old car; don’t discount connection/ground problems in the process of your troubleshooting (I’m an expert troubleshooter, btw).
And don’t let friends that ‘say’ they know 12V systems modify/wire your car for that hot amp or other accessories...electrical problems that result sometimes are never solved...