Brand new battery, brand new alternator, battery light still on after resetting it

If the voltage is fine, then it does not need an ecm.

Thats why I want the actual voltage

Roy

It could be the alternator or the battery failing.
I would have them both checked, most major parts stores will do this for you free of charge.
Let Me know,
Dan

Measure the two voltages on the small wires on the back of the alternator while the engine is running AND while the light is on. Holler back with those numbers.

Wait until the problem occurs, then measure the voltage on the two small wires on the back of the alternator. They will be two wires that are plugged in, or two wires that go through a black plastic block, then appear on two tabs that are held on with two very small nuts. The voltages will only be there when the engine is running.

One terminal must have full battery voltage. The secret is the other wire. It should be less than the first one but not 0 volts. Use an inexpensive digital voltmeter to measure them, then holler back.

Caradiodoc

Yup. REAL common problem. The brushes are worn and making intermittent contact. The testing has to be done while the problem is occurring. During their test, they caught it while it was working.

If you can find the parts, you might be able to replace the brush assembly without removing the alternator from the engine, at least that could be done on the older stuff that I drive. I've done this many times on cars I put "bugs" in for my students to troubleshoot.

Here's a photo of what the assembly looks like. You don't have to remove the terminal block as I did in the photo, just the three screws.

Caradiodoc

Here's what the back cover should look like on your car. Notice the "ND" in the middle for Nippendenso.

Caradiodoc

Is the battery going dead? I really question the fuel pump is the problem. Did they test the alternator?

More then likely you have an issue on the generator field control wire. Either a connector issue or the wire itself has a short or high resistance. I highlighted here in the wiring diagram.

We need to check for a short and measure resistance from end to end. Basically this is the wire that the PCM uses to control the generator.

We can confirm the generator is causing the light to come on if you check the voltage across the battery when the engine is running. There should be around 14 volts. If not then the light is coming on properly telling you the voltage is low.

Let me know what you find. Thanks

https://www.2carpros.com/articles/how-to-check-wiring