'75 280Z Alternator Upgrade (to ZX)

[Tennesseejed]

I recently did the ZX alternator swap on my '75 280Z and thought a brief write-up might be helpful to the HybridZ community.

 

One of the best, and most popular, alternator upgrade threads is found on AltanticZ: http://atlanticz.ca/zclub/techtips/alternatorswap/index.html While the write up looks comprehensive, it doesn't work for the '75 (or at least my car).

 

Here's why:

 

 

This picture is the harness side connector to the external voltage regulator. Notice anything? How about five wires. There is no #1 wire on my harness. Because I wasn't able to find any information on HybridZ or the interwebs about the 'five wire' conversion, I want to pass my learnings on to other who aspire to ditch their external voltage regluator. In addition, what I learned de-mystifies the alternator swap for folks who aren't experienced with electricity and applies to any model Z with an external regulator.

 

Here is what you need to do:

 

1. Source an '81-83 ZX alternator and install. Wire the alternator exactly as your current alternator. There is a battery wire, an earth ground as well as the "T" connector. These wires don't change.

 

2. Access your voltage regulator and disconnect the six wire connector. Clip the wires on the harness side connector as close to the connector as possible.

 

3. Using a voltmeter, find the wire that has battery voltage (+12VDC). One wire will have battery voltage on it without the key in the ignition. This wire is connected to the wire that connects to "N" on the T-connector. "N" and "F" are marked on the back of the alternator. For example, on my '75, the "N" wire was yellow and the white wire going to the harness side connector had +12V. Connect these. Done. Don't be concerned about wire color. If the wire has unkeyed +12VDC battery voltage, it gets connected to the "N" wire on the T-connector. The color of the wire doesn't matter.

 

4. Determine the color of the The "F" wire on the T-connector. This wire gets connected to either (1) Switched +12VDC (Key "ON") or (2) Switched +12VDC (Key "START"). You determine the correct wire(s) by testing each [skip Black because its ground and the battery +12VDC because you are already using it] to see if it has battery voltage when the key is switched to "ON" or "START" respectively. To test for key "START" disconnect the solenoid wire to your starter if you don't want the car to turn over. You can connect either the switched "ON" or "START" to the "F" wire. However, if you have a switched "START" wire, try that one first because you may not need the diode.

 

5. If your car does not have a switched "START" wire, as my '75 did not, you need to purchase and install a 1N5402 (I used 1N5404) diode. The diode has a solid line on one end. Here is all you need to know about installing the diode: The solid line end of the diode goes toward the alternator. Connect. Done.

 

I can't understand why anybody with an external voltage regulator has not done this swap. Especially when I spent $115 for my last voltage regulator and the reman ZX alternator was only $50.

 

Edit: Edited to add that the switched START wire may not need the diode rather than will not need the diode. My car did not have switched START power at the harness connector so I cannot state that for certain. Just a hunch.

Edited August 14, 2012 by Tennesseejed

[daddydonuts]

Good write up, I am buying the conversion plug from MSA to make it easier to install on my 73

Edited August 14, 2012 by daddydonuts

[Leon]

Excellent job! This will be useful when I get to converting my early 260Z.

[NewZed]

Some of the Z's run the Brake Check Lamp Warning Relay power through the regulator. On the 76 cars you can end up with the relay powered all of the time after wiring for the conversion. This will kill your battery in a day or two. You can confirm by listening for the click of the relay, under the passenger seat, when you disconnect and reconnect the battery.

 

76 has the voltmeter instead of ammeter though, so the wiring may not be the same for the check relay. Something to look out for though if your battery starts dying.

Edited August 14, 2012 by NewZed

[Tennesseejed]

Some of the Z's run the Brake Check Lamp Warning Relay power through the regulator. On the 76 cars you can end up with the relay powered all of the time after wiring for the conversion. This will kill your battery in a day or two. You can confirm by listening for the click of the relay, under the passenger seat, when you disconnect and reconnect the battery.

 

76 has the voltmeter instead of ammeter though, so the wiring may not be the same for the check relay. Something to look out for though if your battery starts dying.

 

That's a good point. Some models may have loads that are only part of the charging circuit when the car is running (the voltage regulator is an open when not operating). And by removing the open (voltage regulator) those loads become part of the circuit when the car is not running. Ergo, the dead battery syndrome.

[Akira]

5. If your car does not have a switched "START" wire, as my '75 did not, you need to purchase and install a 1N5402 (I used 1N5404) diode. The diode has a solid line on one end. Here is all you need to know about installing the diode: The solid line end of the diode goes toward the alternator. Connect. Done.

 

My Z is the same year and I also have only 5 wires going to the voltage regulator. I don't understand where you installed that diode. Can you take a picture of it? It would be super helpful for us visual people.

[Tennesseejed]

My Z is the same year and I also have only 5 wires going to the voltage regulator. I don't understand where you installed that diode. Can you take a picture of it? It would be super helpful for us visual people.

 

Since the diode is wrapped in electrical tape, a pic isn't going to help you much.

 

Sorry to be non-visual but the diode goes anywhere inline with the Switched 12V wire and the "F" wire on the alternator. The doide has a white line on one end. This end of the diode goes toward the alternator, i.e, attached to the "F" wire.

 

You can't harm your car by installing the diode incorrectly or by not installing it at all. The diode simply blocks feedback current which causes the 'run on' syndrome.

 

Good luck.

[cd1105]

I did this mod a while back on my late model 260z and I have to problems shutting off my car with the key. My question for anyone that has done this swap is how do you know that the alternator is actually charging the battery correctly? Is the charging light supposed to light up on the dash? If so, mine does not. I plan on driving my car(260z with l28et swap) for the first time in a few weeks and everything runs fine, but this has always been in the back of my mind, so i would like to address the issue if there is one, before I drive my car, turn it off and be stranded because of a dead battery

[Leon]

There is a simple test procedure in the FSM, in the Charging section of chapter EE.

[Tennesseejed]

I did this mod a while back on my late model 260z and I have to problems shutting off my car with the key. My question for anyone that has done this swap is how do you know that the alternator is actually charging the battery correctly? Is the charging light supposed to light up on the dash? If so, mine does not. I plan on driving my car(260z with l28et swap) for the first time in a few weeks and everything runs fine, but this has always been in the back of my mind, so i would like to address the issue if there is one, before I drive my car, turn it off and be stranded because of a dead battery

 

 

Test the DC voltage across your battery terminals with all wires attached.

 

Turn your car on and let it idle. Test your DC voltage across the positive and negative battery termainals again. You can also rev your car a bit by reaching over engine and cracking the throttle.

 

If you're reading ~14.5VDC while the car is running, your alt is charging.

 

I'd have to look at the schematic to be sure, but the charging light might be isolated by cutting the other wires from the external regulator. On my '75 280 the voltage gauge still works as it did before.

Edited October 24, 2012 by Tennesseejed

[cd1105]

Test the DC voltage across your battery terminals with all wires attached.

 

Turn your car on and let it idle. Test your DC voltage across the positive and negative battery termainals again. You can also rev your car a bit by reaching over engine and cracking the throttle.

 

If you're reading ~14.5VDC while the care is running, your alt is charging.

 

I'd have to look at the schematic to be sure, but the charging light might be isolated by cutting the other wires from the external regulator. On my '75 280 the voltage gauge still works as it did before.

Thank you, I will try tomorrow.

[cd1105]

Tested my battery for its voltage while idleing and reving it a little, and my alternator is for sure not charging it. DC voltage reads about 11.8. I might just have a bad alternator(Getting it tested tomorrow). I have a question about how the system recharges the battery though. My battery is relocated to the trunk, and the positive and cable goes through the firewall and into the engine compartment and onto the starter bolt. Does the alternator recharge the battery directly through the postive cable, or is there another wire that was originally on the postive post of the battery that leads into the charging system?

 

The pictures below is how the battery is hooked up in the hatch and the connection at the alternator, does everything look right?

 

 

 

[NewZed]

Typically the W/R wire from the back of the alt terminates at the starter lug, after feeding the fusible links along the way, the same point as the positive battery cable, and charges the battery through that point.  If you only have your positive cable connected to the starter and no other wires to battery positive, then your battery won't get a charge.  But your engine shouldn't start either since you'll have no excitation current to the alternator.  But if you only have the EFI supply connected to the battery pos., through the green fusible link, then the engine might start, but not charge, unless it self excites at higher RPM from residual magnetism.  That would probably show as low voltage at the battery, but regular charging voltage at the fusible links or alternator post.

 

What else is connected to the battery positive post or the starter lug?

[Xnke]

For reference, gentlemen, you aren't gaining anything with the ZX alternator swap anymore. All rebuilt ZX alternators that I have been able to source in the last two years (sample size six, from two different suppliers) are 60A units...So at best, you're eliminating the external regulator.

 

If that's the goal, well, you might look into the KA24E alternators as mounted to the Nissan D21 trucks too. Early ones are 60A, and are the same unit as the ZX, but later ones (I haven't figured out the year split) are 95A units, with a similar 3-wire hookup and a weatherproof harness connector.

Edited January 28, 2013 by Xnke

[NewZed]

That is true.  If you're replacing both VR and alt, money is saved, if you only need to replace one, probably not worth it just replace the bad part.

 

Interesting tip on the pickup alternator.  I browsed through RockAuto and found that 90 - 95 pickups (Edit - with the VG30 engine, the 2.4Ls were at 60 amps) seem to have the same shape, with a pully instead of the ribbed belt, but a different electrical connection,.  But they are 70 amp, so for a little wiring work you could gain 10 amps on the high end with a bolt-in swap, and some rewiring.  That's probably a better value since wires will be spliced anyway in the swap.  Easier than swapping pullies on the Maxima alternator.  It should probably be THE alt swap to do if anyone is going to do it instead of the ZX swap.

 

I couldn't find a reference to a 95 amp alt though.

 

To cd1105's post point - he's already in it and just trying to make it work.

Edited January 29, 2013 by NewZed

[Dan_Austin]

The early 90s Maxima has a 90 amp that is a physical bolt in

that needs a pulley swap and minor wiring mods.

 

I checked with a local rebuilder to get one that was not rebuilt

to parts bin standards, and they recommended a CS130 from

and 89-94 Dodge Monaco (which appears a rebadged Renault).

It also is a physical bolt-in with a pulley swap and minor rewiring.

It is rated at 105amp and can be reconfigured up to 140amp

reliably.  I did not need much more that the 60 amp unit I was

replacing, so I went with the 105, and according to its test sheet

it was actually a bit hot at 117amp.  If you can handle the wiring to

convert from external to internal regulation, you can handle the

Maxima or this CS130 swap.

Edited January 29, 2013 by Dan_Austin

[Tennesseejed]

For reference, gentlemen, you aren't gaining anything with the ZX alternator swap anymore. All rebuilt ZX alternators that I have been able to source in the last two years (sample size six, from two different suppliers) are 60A units...So at best, you're eliminating the external regulator.. . .

 

Xnke, the last Z alternator I bought was ~$50.  The last external voltage regulator I bought (locally) was ~$115.  Without question, my primary goal was to simplify and stabilize my electrical system.  Folks that want big amp alternators might look into the GM conversion too. 

 

@cd1105, sorry to hear you haven't worked the bugs out of your charging system yet.  I've had a little to much wine tonight to talk electrons, so I'll try and look at your issue tomorrow and give you my thoughts.  Let us know how the alt test goes.  Last alt I bought - for a Dodge pickup and it was guaranteed 100% tested - had a bad diode and went back the next day.

 

@cd1105, NewZed pretty much answered your question in Post #13.  The W/R wire on the back of the alternator is the output, and needs to be attached to battery positive.  If you haven't already removed/tested your alternator, I'd put a voltmeter on the W/R terminal or wire with the car running and see if you are getting more than battery voltage.  If so, you solution might be as simple are connecting the W/R wire to battery positive.

Edited January 29, 2013 by Tennesseejed

[cd1105]

Xnke, the last Z alternator I bought was ~$50.  The last external voltage regulator I bought (locally) was ~$115.  Without question, my primary goal was to simplify and stabilize my electrical system.  Folks that want big amp alternators might look into the GM conversion too. 

 

@cd1105, sorry to hear you haven't worked the bugs out of your charging system yet.  I've had a little to much wine tonight to talk electrons, so I'll try and look at your issue tomorrow and give you my thoughts.  Let us know how the alt test goes.  Last alt I bought - for a Dodge pickup and it was guaranteed 100% tested - had a bad diode and went back the next day.

 

@cd1105, NewZed pretty much answered your question in Post #13.  The W/R wire on the back of the alternator is the output, and needs to be attached to battery positive.  If you haven't already removed/tested your alternator, I'd put a voltmeter on the W/R terminal or wire with the car running and see if you are getting more than battery voltage.  If so, you solution might be as simple are connecting the W/R wire to battery positive.

 

Thanks for the quick answers you guys. I have the main R/W harness wire hooked up to the starter lug as well as the two fusible link wires(green and brown i think), along with the positive cable from the positive post on the battery. I'm assuming that the big R/W wire from the main harness closest to the starter lug(and also connects on the starter) is also connected to the R/W wire that goes to the back of the alternator(Or is it the same wire)? Is that how the alternator charges the battery, when the R/W wire and the positive cable are connected to the same point on the starter?

[gijohnny23]

I would just like caveat this for the 85 300zx connector/alternator upgrade ie basicly every nissan plug up to 95 I've found. With the locking tang facing up looking at the connector backing. The left side is 12v ignition the right side is constant 12v. I still don't know if the constant requires some sort of resistance normally caused by the dummy light but for us 75 guys who don't have one I will be adding an led one soon. Mostly because I can't find the 77-78 voltmeter to install.

[2turboZ]

Found this on a search since I am swapping a turbo engine and ZX Alternator into my 75 (1/75 build date). 

 

I had 6 wires and they were different than any of the 3 write-ups I found online.  I ended up following the OP's direction and ended up jumping 2-3 and 5-6 with a diode in the 5-6 splice since it was key-on hot.

 

My conclusion is that Datsun changed wiring frequently.  Don't just count terminals and think it will work.  Verify what you have at each wire before splicing.