"Pulsing" voltage, RPM drop with load.
The 72 ammeter I think is still 40 amps to 40 amps.
So if you saw deflection toward charge about 20% from center, that's about right.
Then it went to center when there charging was complete.
If the alternator can't supply the power, the ammeter needle should go toward discharge as the battery takes over.
It should have done that even with jumper you put it on. The path from the battery through the ammeter is shorter and normally less resistance than following the jumper to the alternator stud, then to the bulkhead.
If you have long enough leads on your meter you can measure voltage difference between the alternator stud and other connections directly. But for first checks I like to just measure voltage to ground.
When there is no flow, the voltage will be the same everywhere. So with everything off, the alternator stud, battery positive and all the wires in between should be at the same voltage even with a bad connection.
Its just like pressure. If there is 12.8 psi on one end of a closed pipe, its 12.8 psi throught the pipe.
It doesn't matter if inside the pipe there is a partial blockage. It's still 12.8 psi throughout.
If we could look inside, the pressure on both sides of the blockage would be 12.8.
Connecting that same pipe to an air gun or an impact wrench and lets see what happens to the pressure.
There's still 12.8 psi supplied, but on the other side of the restriction the pressure is lower. The more air being used downstream, the more the pressure drops.
The 72 ammeter I think is still 40 amps to 40 amps.
So if you saw deflection toward charge about 20% from center, that's about right.
Then it went to center when there charging was complete.
If the alternator can't supply the power, the ammeter needle should go toward discharge as the battery takes over.
It should have done that even with jumper you put it on. The path from the battery through the ammeter is shorter and normally less resistance than following the jumper to the alternator stud, then to the bulkhead.
If you have long enough leads on your meter you can measure voltage difference between the alternator stud and other connections directly. But for first checks I like to just measure voltage to ground.
When there is no flow, the voltage will be the same everywhere. So with everything off, the alternator stud, battery positive and all the wires in between should be at the same voltage even with a bad connection.
Its just like pressure. If there is 12.8 psi on one end of a closed pipe, its 12.8 psi throught the pipe.
It doesn't matter if inside the pipe there is a partial blockage. It's still 12.8 psi throughout.
If we could look inside, the pressure on both sides of the blockage would be 12.8.
Connecting that same pipe to an air gun or an impact wrench and lets see what happens to the pressure.
There's still 12.8 psi supplied, but on the other side of the restriction the pressure is lower. The more air being used downstream, the more the pressure drops.
