Rolling back to the original alternator wiring thread - seems like the L wire going open circuit might cause the ammeter issue.  Might be two separate issues here, a dying starter and problematic wiring.

How about some current pictures of the alternator and its wiring today?  Especially the L circuit wire.  Might be illuminating.  

 

Actually, I might have my ammeter signs backward.  Could be S is going open, as SteveJ suggested.

Anyway, my point was about the possibility of funky wiring.

Ok, more info.

-the red wire from the starter is fused, and leads to a relay at the firewall. didn't trace further yet, can do if relevant. see pics.

-the starter solenoid wire is fully burned through in one spot.

-I am really going off memory, but I believe the 6 pin plastic cap at the voltage regulator location was bought from one of the more prominent Z car retailers, specifically for use with an internally regulated alternator.

-the starter gear spins freely, and the teeth show no wear. 

 

-I recently bought a big battery charger that has an alternator test mode of some sort; maybe I should test the alternator to verify it's efficacy?

Edited September 29, 20231 yr by RJK

Well guess who has the Frontier alternator.

Your alternator is connected properly, too. I just verified against my car. However, the crimped lug on the red wire is curious looking. If I can remember, I will make a video to show you how to verify the wiring. 

When you say that the wire burned through, are you taking about the wire between the solenoid and starter? If so, look on RockAuto for a 280ZX starter. They have some listed as new.

 

Thanks Steve! I'll pull the connector on the alternator and throw a DVM on the red wire to its termination point, and see if I can't verify that crimp.

 

yes, the wire between the solenoid and starter, that looks charred, is actually burned through the insulation in one spot. Rock Auto lists this; I do not know Wai Global" as a manufacturer..

 

https://www.rockauto.com/en/catalog/nissan,1978,280z,2.8l+l6,1209260,electrical,starter+motor,4152

Here's how you should check the voltage. Make sure the 6 pin connector is plugged in.

1. Unplug the connector from the alternator. Measure voltage to ground at the red wire and green wire. The red wire should have battery voltage. The green wire should not.
2. If the first test passes, put the key in ON. Measure voltage to ground at both wires again. This time both should have battery voltage.

The starter you linked was the one I was referring to. It's difficult to find parts not made in China.

After you fix your starter and get ready to run your car again, make sure you measure the voltage while the car is running at the alternator and then check at the battery. I'm starting to think there are some problems lurking in your car that you may need to address. If the voltages are significantly different, that would confirm my suspicions.

Edited September 29, 20231 yr by SteveJ

Thanks Steve! So the car passed your test, and did as hoped at the green and red wire of the alternator connection. I don't know if this was an issue before, or one i implemented BY testing, but the blade of the cars wiring harness was popped out of the connector, so initially the test failed. After diagnosing, I found the blade to be just out enough to not conduct. Pushed in, re-tested, works as hoped.

 

Please see video of both DVM at the red alternator wire as connected, and the dash ammeter. This is with the new "pure energy" starter installed. It's definitely not pegging now. This is just a cursory "in the shop" 30 second test, I havent put the car through any paces, but does this look normal-ish to you all?

32 minutes ago, RJK said:

Thanks Steve! So the car passed your test, and did as hoped at the green and red wire of the alternator connection. I don't know if this was an issue before, or one i implemented BY testing, but the blade of the cars wiring harness was popped out of the connector, so initially the test failed. After diagnosing, I found the blade to be just out enough to not conduct. Pushed in, re-tested, works as hoped.

 

Please see video of both DVM at the red alternator wire as connected, and the dash ammeter. This is with the new "pure energy" starter installed. It's definitely not pegging now. This is just a cursory "in the shop" 30 second test, I havent put the car through any paces, but does this look normal-ish to you all?

IMG_6742.MOV

A loose connection could have caused issues.

How and where were the meter leads connected to the electrical system in your video. The meter certainly was jumping around. You may want to test without video to see what the voltage is. I did see it popping up to a little over 14, so if it is staying in that range, that should be good.

I'm wondering if the ammeter is off or if you really are pumping out as much current as it's reading. It's not a precision gauge, but that looked to be around 20A, maybe more.

I would expect to see that if there are a lot of loads on the battery side of the ammeter (I'm still curious about that red wire.), or a battery that is going south or had been greatly discharged. You may want to put the battery on a charger for a few hours and pull the fuse on the red wire. Then see if the ammeter is still reading like that.

@SteveJ a million thank yous!!! extremely helpful tips here, kudos for all your info.

 

I had the ground of the DVM alligator clipped to the battery ground terminal, and the positive lodged inside the molex connector(red wire) that leads from the alternator. battery was fully topped off from a trickle charge before i made this video. will pull the fuse on red wire tomorrow, test, and see where ammeter lands. battery is 2021, and i am pretty strict about keeping my old cars on trickle chargers.

Yeah, run a test with you holding the positive meter lead firmly on the battery post while the car is running and warmed up. If the voltage is below 13.5, reach across and operate the throttle slowly while looking at the meter. See if the voltage will hover more in the 14 volt range.

Please trace out that red wire. I'm wondering whether someone "fixed" the wiring in the past or just added things.

Well I think I have good news. I pulled the fuse for the red wire at the starter, and it's the fuel pump. I was able to briefly run the car without, and the ammeter definitely hovered much closer to the midpoint. the previous owner installed a fuel pump that is quite loud; I don't know if I've ever heard one this loud. There's an aftermarket cutoff switch in the car, which is actually nice from a safety POV.

 

I re-installed the fuse and ran the car til everything was hot and "run in".  Attached is where the ammeter needle stayed stable.This seems better, no?

That certainly explains the ammeter reading.

The reading in your latest photo seems to show the fuel pump draw if the battery was fully charged given how you say everything is wired.

What is the voltage reading with the battery topped off and car running?