New 280zx Alternator Swap not charging 240Z.

[5 Star Rising]

I have a early 71 240z that is not charging the battery I checked all the fuses behind the ash tray and they were good (PO added a aftermarket fuse box with spade type fuses)....

 

I took the stock alternator down and it tested bad at the parts store, so I ordered a rebuilt replacement and installed it. It still didnt charge the battery, I swapped 2 other old external voltage regulators that I had on different parts cars and still no charge at battery (guess they could have all been bad). The reman alternator was putting out like 40 volts out of the back of it ,seems like a bit much.

 

Changed plans and returned that first reman alternator and decided to go with the 280ZX alternator upgrade instead. I installed the 280ZX alternator and I also bought the little diode plug adapter from Z Car source and plugged it into my factory harness..I'm getting around 16 volts off the alternator now but it's not charging the battery only getting like 11.9 volts at the battery.  Has anyone ran into this issue? What could be going wrong here? Advice would be much appreciated.

[calZ]

Your car still has an ammeter, not a volt meter, correct? Someone might correct me, but I believe all the alternator current flows through the ammeter, so if your gauge is fried it would block the current and prevent any charging at the battery. 

[5 Star Rising]

8 hours ago, calZ said:

Your car still has an ammeter, not a volt meter, correct? Someone might correct me, but I believe all the alternator current flows through the ammeter, so if your gauge is fried it would block the current and prevent any charging at the battery. 

Yes it has its factory Ammeter in place. How would I test it? Measure resistance? 

[NewZed]

15 hours ago, 5 Star Rising said:

I'm getting around 16 volts off the alternator now but it's not charging the battery only getting like 11.9 volts at the battery

 

The B+ terminal where you would be measuring the 16 volts should be connected to the battery positive post through the lug at the starter.  There is a fusible link in the circuit.  Use your meter and check the circuit.  Follow the wire from the alternator to the battery post.  Check the fusible link.

 

Looks like Nissan ran the circuit through the fuse box on the way to the starter.  The ammeter is on a parallel circuit, called a shunt, that would not control current to the battery.

 

 

 

Edited February 23, 2022 by NewZed

[5 Star Rising]

Ok so I found the problem.  I checked continuity from the main power wire from the alternator and followed it to where the in and out connection is for the Ammeter under the glove box passenger kick panel area. The 2 Spade connections for the Red/White wire and White wire were really corroded and not making a good connection, I cleaned the female and male spade connectors and now I get 13.85 volts at the battery. With just the ignition key on but motor not running you could jiggle the wire connections and here the relay kick on and off due to the bad connection..The only thing that concerns me is this is a 60 amp alternator replacing the 45amp? The spaded wires are warm to the touch when the car is running, alittle more amperage on those wires I guess.  looks like they got alittle hot before though with the 45 amp alternator as one of the clear plastic connector sleeves was slightly melted and discolored. I'm going to keep an eye on it.

 

Now to move on to another issue on this damn car. Never been able to get the carbs to run right with SUs and now with Triple Weber's also. While the car was running earlier the oil dip stick shot out and it sounded like I cut the valve stem off a bicycle tire. Haven't dug into this yet but this could be bad..  A stuck valve perhaps? Might post this in another part of the forum if I get stuck diagnosing it.  Thanks for the alternator info..