280z Alternator Grounded?

[TakemuraShuu]

Hi, I have a 78 s30. Been working on the car recently and noticed the alternator isn't charging the battery, and the red charge light is on w/ the voltage reading about 6 on the stock gauge. When the car is running w/ no accessories on, voltage of the battery is at around 12.2-12.35v.
Read through the electrical section of the FSM. With the car running, POS point on tester to battery, and NEG point of tester to the point on the alternator that says BAT, the tester reads 10.35??? This doesn't seem right, A pos and a pos shouldn't read a voltage like that, right? Think the alternator could be grounded out somewhere in the 40+ year old wiring? This alternator is 10 months old.

[TakemuraShuu]

Also forgot to add, if I unplug the "T" plug the charge light goes off, but not still not producing anything from the alternator. If I use a jumper wire with one end on the POS terminal of the battery, and the other end touching the top pin on the alternator that the fatter white/ with red stripe wire that goes to the "T" plug, there's a spark, voltage drops, then car shuts off. Assuming that it grounded for some reason. When car is off, battery is at 12.6, when running it drops to 12.3

Edited April 26, 2019 by TakemuraShuu

[NewZed]

4 hours ago, TakemuraShuu said:

With the car running, POS point on tester to battery, and NEG point of tester to the point on the alternator that says BAT, the tester reads 10.35??? This doesn't seem right, A pos and a pos shouldn't read a voltage like that, right?

 

I think that shows a high resistance in the line from the BAT terminal to the battery.  That cable runs to the starter lug, then the positive cable runs up to the battery.  Could just be a loose connection at the starter terminal or bad positive connection at the battery.  It's a good test though, you have a problem somewhere along the way.

 

Forgot about the black fusible link also.  It could be bad or have a bad connection.  It's on the way to the battery from the BAT terminal.

Edited April 26, 2019 by NewZed

[NewZed]

3 hours ago, TakemuraShuu said:

Also forgot to add, if I unplug the "T" plug the charge light goes off, but not still not producing anything from the alternator. If I use a jumper wire with one end on the POS terminal of the battery, and the other end touching the top pin on the alternator that the fatter white/ with red stripe wire that goes to the "T" plug, there's a spark, voltage drops, then car shuts off. Assuming that it grounded for some reason. When car is off, battery is at 12.6, when running it drops to 12.3

 

 

The leg of the T should be white with a black stripe by the diagram.   The other should be yellow.  The WB wire is the one that should control your charge light.  Not sure what's happening when you jump it like that, it shouldn't really do anything.  It might be that you're running full current through a short in the alternator.  The charge light is actually a resistor that controls current flow through that circuit.

 

Kind of sounds like you have two problems - a bad connection to the BAT terminal, and a bad alternator.  Parts store alternators have been known to be bad out of the box.  I'd get it tested.

 

 

[TakemuraShuu]

8 hours ago, NewZed said:

 

The leg of the T should be white with a black stripe by the diagram.   The other should be yellow.  The WB wire is the one that should control your charge light.  Not sure what's happening when you jump it like that, it shouldn't really do anything.  It might be that you're running full current through a short in the alternator.  The charge light is actually a resistor that controls current flow through that circuit.

 

Kind of sounds like you have two problems - a bad connection to the BAT terminal, and a bad alternator.  Parts store alternators have been known to be bad out of the box.  I'd get it tested.

 

 

First off thanks so much for replying NewZed, you've helped me in the past as well. Second, I think the wiring on this car may have been changed in the past. On the diagram where the "Y" wire is on the "T" plug, mine is a thick white wire w/ a red stripe, and "WB" wire on the diagram is a slim blue wire on my car. Sounds strange.

 

Anyway I'll remove the alternator and take it to the parts store to see what the deal is with it. Thanks again!

[TakemuraShuu]

Alternator was shot, even though it wasn't even a year old yet...

[TakemuraShuu]

Installed new ZX alternator
-With car idling-
Voltage at Alternator(+ on BAT, - on Battery Negative Terminal)- 14.65v
-
Voltage at Battery(+ Battery Positive Terminal, - on E) - 12.49v

Also car stays on for a while after turning key to OFF position.
With key in OFF, will still be car running, however unplugging the "T" plug for the alternator shuts the car down.
Pretty sure the Battery and Alternator should read the same, but they aren't. Looked at the fusible links and they look fine.
Read over the FSM, and can't seem to find anything that would give me a lead. Back at square one.

Edited May 9, 2019 by TakemuraShuu

[jhm]

Yes, your battery should read 14+ volts when running, if the charge system is functioning properly.  Have you measured resistance from the alternator to the battery, as suggested by Newzed?  That could help you track down where the losses are occurring.

 

Also, how long is "a while", that the car continues to run after turning the key off?

 

Finally, it seems you believe that a PO has modified the wiring to your tee connector; but have you traced the wiring from end to end?  That's really the only way you'll know for sure if they mucked something up when they rewired it.