The brake and battery light come on at the same time it. It doesn’t come on at idle, and the voltage is perfect. As soon as I barely tap the gas, the light starts flickering very fast and it starts undercharging. the higher rpms I go to, the more solid and bright the light becomes and worse it undercharges.
I’ve cleaned every ground, got new battery terminals, brand new oem alternator, checked all fuses, and still nothing fixed it.
the only thing that seems to do something is when I unplug the voltage regulator connection on the alternator, clean it, and plug it back in. It runs normal, at perfect voltage, but the next time I start it after a few hours it goes back to undercharging.
what can I even do i don’t know what else to try

 

Check the engine-chassis bonding jumper, definitely sounds like a ground problem.

That jumper is the larger gauge wire that lands on the right side of the timing chain cover that goes to the chassis directly under the coolant reservoir. 1 hole lug on the timing chain cover side, 2 hole lug on the chassis.

Also, did you clean the negative battery cable where it attaches to the chassis? Same 2 hole lug as that other wire.

 

yeah I cleaned both of those with a dremel and sand paper

 

Just out of curiosity do your battery POSTS on the battery feel tight or is there a tiny bit of play in it? You could have internal damage on the battery.

Also, how many volts is the system at idle?

You say you got another OEM alternator, you mean you purchased it FROM NISSAN correct? Not eBay, not a Facebook marketplace, but from the actual dealership in your town yes?

 

the battery posts are good. I also just had the battery checked last night and they said it was good.
it runs at ~14.2 at idle
I bought the alternator from z1 motorsports they sell oem stuff and the box was the Nissan group genuine parts box.

 

Ok Z1 definitely sold you an OEM unit, your 14.2v is correct. I'm think you need to check the ground wires in the dash, there's one by the ignition cylinder that's for the instrument cluster, another behind the stereo that's for the stereo and ECM.

If you have an aftermarket head unit then just start with that one behind the stereo first, probably didn't get tightened back down properly when the aftermarket HU was installed.

 

i replaced the whole dashboard before so any of those could be it I will check when I get the chance.

 

I can’t find the grounds, could you tell me specifically where they are, I tried to look but i dont know exactly where they are or what they look like

 

Big green colored bolt behind the instrument cluster near the ignition cylinder, glove box, sorry I said behind the HEAD UNIT earlier which is not correct and I keep forgetting on the G ECM ground is behind the GLOVE BOX.

Here's the one behind the instrument cluster. Since it's a multi-term crimp I would get in there and inspect this one pretty thoroughly to make sure all the wires are snug, a little tug test is probably sufficient. This is my primary suspect, it is the ground for your dash.







Next, the ECM ground MIGHT be the culprit though, it's a lot more accessible than the one behind the instrument cluster so this is TYPICALLY the one that causes issues for people because of not tightening it properly after adding other ground wires to it for various other cabin electronics.

Here are two pictures of it.








Next, and I'll bring it up again even though I think you already checked it, the engine bonding jumper IS the alternator ground wire. It lands on the timing chain cover on the right side of the engine, then lands on the chassis on a 2-hole lug directly below the coolant reservoir.







Lastly, if you haven't also checked the battery negative 2-hole lug on the chassis you should.

 

You should also check the positive side of the alternator circuit which fortunately is much simpler.

First check the primary where it attaches onto the fusible link, I strongly recommend completely disconnecting the fusible link so you can really get a good look at this thing especially INSIDE where the fuse goes to make sure it's pins aren't corroded. Primary charging is on the big wire I circled in red, the feedback loop BACK TO the alternator voltage regulator is fuse 36. If there is corrosion on the fuse or damage to the fusible link the alternator might be reading actual voltage incorrectly and wrongly cycling the regulator. However you would usually see something wrong with a digital multimeter, still something you should inspect though...

Keep in mind that the dash light will turn on from both under voltage (more common) as well as OVER VOLTAGE which can occur if there is resistance and corrosion on that feedback loop back to the regulator, or if the circuit is just stuck open due to a blown fuse or something. You can accidentally charge a battery up to about 18vdc (the extreme upper end of what an alternator can usually make) which makes them VERY hot, most of the electronics will survive at 18vdc though, your fuel pump will be hating life and delivering too much pressure and flow at that voltage though. I imagine the instrument cluster on the G35 is designed to turn on the light at lower than 11.5v or higher than 15.5 volts. Never tested it but that's usually where lights turn on with other vehicles.







Next is the monitoring circuit for the instrument cluster, cabin Fuse Block - J/B fuse 14 (10amp) supplies power to the instrument cluster voltage monitoring circuit, ground goes directly back to the alternator (through a super multiple junction).

I doubt the fuse is the issue and I think the light would not turn on AT ALL if the fuse was blown.

 

I’m having the same issue did you ever find a solution?

 

Yeah its been good for over a year now. It was just the alternator apparently. I went through probably 3 including 1 oem from z1 but none of them worked. I got a 4th one from O'reilys and it worked. Apparently a "new" alternator failing prematurely is more common than most people think. You just gotta keep switching the alternator out until you get a good one. It just sucks because its a pain to switch them out in our cars.
Id also recommend checking and replacing your battery terminals if they look bad; another theory is that the alternators kept going bad because my terminal was bad.

So Id just make sure your positive and ground terminals are good, make sure all your fuses are good, then find a alternator that actually wants to work (hopefully you get one faster than I did)

 

alright I’ll try getting a new one and checking the battery terminals, thank you