Alternator Upgrade Issue

[eastcoastz]

Hello.  I wanted to upgrade my original alternator, so I purchased a 60A alternator from a 280zx and installed it.  I cut off the connector on the external voltage regulator and jumped the two pins like the following diagram that I found (yes, I have made sure, multiple times, that the diode is in the correct direction).

 

The issue that I'm having is that when the alternator is connected, it drains the battery when the car is off.  If I connect the alternator and then hook a multimeter to the battery, it drains .01V every 2-3 seconds... and eventually completely depletes the battery.  If I unplug the jumped connector (or if I unplug the two ping S/L connector on the alternator), the draining stops.

I'm waiting for a replacement alternator to see if it was the alternator causing the issue, but I wanted to see if anyone has every had/heard of this issue before?  I had read that if a diode goes bad in the alternator, then it can drain the battery while just sitting (off).

Thank you!

[SteveJ]

Please post the year of your Z. That could provide important information. As a matter of fact, it wouldn't be a bad idea for you to create a signature with that information.

[eastcoastz]

Thank you.  I have a 1971 240z.... I purchased a 60A 280ZX alternator (BBB Industries - Part# 14592).

[Zed Head]

1 hour ago, eastcoastz said:

I'm waiting for a replacement alternator to see if it was the alternator causing the issue,

You can use a meter to see if there's a short through the alternator.  You should be using a meter anyway when modifying wiring.

[SteveJ]

Yes, a bad diode would allow the battery to drain. This can be tested with a voltmeter.  With the key off, insert the positive probe of the meter on the black/white wire (where I have the arrow). Put the negative probe on the battery negative and measure voltage. If you see battery voltage, then the diode is bad or installed improperly.

[eastcoastz]

@Zed Head Yeah I've been using a meter to test the wiring... that's how I found that the battery was dropping voltage when the alternator is connected.  I had read that I could put the meter on the diode setting and put one lead on the battery output (on the alternator) and the other lead on the casing of the alternator.  This is giving a reading of around 1250... I read that if it's a diode in the alternator that's causing the drain, then this reading should be a lot lower (like 250), but some people were also saying this may not be a fool proof way of testing the diodes because an alternator can have 6 (maybe more) diodes inside.

 

@SteveJ I pulled the connector (with the jumped wires) off of the engine harness and the diode tested fine (got a reading of about 580) when I put the meter probes on the pins/blades (that go into the engine harness).  Are you saying that I should probe the black/white wire with the "jumped" connector off (in order to test the diodes inside of the alternator)?

Edited October 10, 2022 by eastcoastz

[SteveJ]

I'm saying it should be tested with everything connected. If you see voltage on the black/white wire with the key off, there is something wrong, and it's probably either a bad or incorrectly installed diode. Other than that, it could be a voltage regulator in the alternator. This is where a clamp ammeter can be handy for testing where current is flowing.

[eastcoastz]

Thanks so much!  I have to wait for the replacement alternator (had to send the first one back already)... so I'll test that black/white wire when I connect up the new one and I'll let you know what I find.

[Zed Head]

You don't have to wait for the new alternator.  SteveJ's tests are for the harness.  The wire that goes to the L terminal would have to have voltage from the battery in order for the battery to discharge through the Lamp circuit.  if the alternator is okay.  Put your meter on the L wire in the harness and see if it has voltage with the battery connected and key off.

The S wire will always have voltage and could only cause a draw if the alternator had an internal short.

Don't overlook that the original wiring might have other devices on the L circuit.  S and L are the labels for the internally regulated alternator systems.  

The top of the T is S, the upright is L.

[Zed Head]

5 hours ago, eastcoastz said:

if I unplug the two ping S/L connector on the alternator

This part does suggest either a bad alternator or a device on the L wire, like a relay, that is powered by the newly jumpered wires.  It would be on the L circuit.  If you measure voltage on the L wire with the key off then the problem is in your wiring.  I had this problem on my 76 with the brake warning lamp check relay but I don't know how the 71's are wired.  It should show on a wiring diagram.

[eastcoastz]

Thank you. I’ll run some test as soon as I can and respond back. 
 

If I’m reading the wiring diagram correctly it looks like the L/S was originally F/N and it looks like those wires just go between the alternator and the (now absent) external voltage regulator. 
 

That being said, I’m not sure what you mean about the L circuit since the L (former F) wire just ends at the voltage regulator. 
 

I never had any battery drain issues with the OEM alternator (and external voltage regulator). I just thought it would be a good idea to upgrade to a 60A alternator and I immediately had this battery drain issue. 
 

Thank you for all of your help!

[Zed Head]

The external regulator acts as a relay for other relays.  When you take it out of the picture and use some of the various wiring diagrams out there for converting you end up closing the circuit to the other relay without realizing it when you jump those wires.

The L pin on the externally regulated alternator is a path to ground.  So if you see voltage on the wire that connects to the L pin, after you wired the jumpers in, with the key off, then the voltage will have a path to ground with the key off.

The S pin sees voltage all of the time, normally.  It is not a path to ground.  Here's 1982 -