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I'm having some charging issues with my '78 280Z and there's so much information on the internet it's kind of overwhelming so I am hoping being able to actually talk with you guys can help!  Was letting the car warm up the other day and then it started running rough and I noticed the volt meter needle was down around 8v. Assumed it was the old alternator that has been on there for who knows how long. Bought and installed new alternator, re-charged battery, and just went to test it again and same thing. The voltage slowly drops as the car is running and doesn't recover on its own. So here's some bullet points.

 

- Car wont hold charge.

- Same problem with old and new alternators

- Battery will take a charge, but it's older too.

- Wire connections at alternator appear to be okay.

- Belt seems newer, good tension, no visible issues.

 

EDIT: FIXED!!! The culprit, a bad Brake Warning Lamp Relay, located under the passenger seat. Replaced with a standard 4-pin relay and wired it up as follows...

86 - Green

85 - Light Blue

30 - Green w/Yellow Stripe

87 - Black

 

The alternator now charges the battery, the CHG light works again, and the brake warning light now works properly. The tachometer still does not work but that is a separate and unrelated problem. Hope this can help someone in the future!

Edited by TheWeekendWagon
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37 minutes ago, TheWeekendWagon said:

- Wire connections at alternator appear to be okay.

 

Get a voltmeter and measure voltage at the plug to the back of the alternator.  The T plug.  They should both show 12 volts with the key on.  Also make sure that plug is making good contact with the pins in the alternator.  I had a plug that was loose and was not making contact.  Had to recrimp it with a pair if pliers.

 

Make sure that the charge wire to the lug on the starter is intact.  It's the white wire that starts at the B terminal on the back of the alternator.  And check your fusible links.

 

 

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43 minutes ago, NewZed said:

 

Get a voltmeter and measure voltage at the plug to the back of the alternator.  The T plug.  They should both show 12 volts with the key on.  Also make sure that plug is making good contact with the pins in the alternator.  I had a plug that was loose and was not making contact.  Had to recrimp it with a pair if pliers.

 

Make sure that the charge wire to the lug on the starter is intact.  It's the white wire that starts at the B terminal on the back of the alternator.  And check your fusible links.

 

 

 

Thanks for the quick reply! Fusible links and starter connection are in-tact and good. The White/Red wire to the T-Plug shows 12V BUT the Light Blue wire on the T-Plug shows nothing so maybe that's the problem? The contact is great and I even put a new terminal end on it to make sure there was zero corrosion at the connection point to the alternator.

 

From the wiring diagram I can see that Light Blue wire is also connected to the following...

Fuel Pump Control Relay - Fuel pump and fuel delivery have no issues.

Voltage Gauge - Seems to be working fine although I am not sure the charge light works as it never came on as the battery drained.

Brake Warning Lamp Check Relay - If this is the light on the speedo that lets you know the e-brake is up, that is permanently on even when the e-brake is down.

 

The brake warning lamp connection may make some sense and leads me to believe I should probably list other issues with the car as maybe there's a connection there that makes sense to someone more educated than I. So I just did a big interior overhaul (carpet, seats, etc.). One of those items I did was change the bulbs in the gauges to LED. They all work but a few new problems, including this one, have arisen since the interior overhaul. Aside from the charging issue and the e-brake warning lamp constantly staying lit the tachometer also doesn't read RPM. The turn signal lamps and such work on the tach, it's just not getting a signal for RPM. I haven't dove into this issue yet aside from double checking my connections at the tach which are good.

 

So what is the purpose of the Light Blue wire coming from the alternator? Does it make sense that there is no power at the alternator but there is power getting to the e-brake warning light and the fuel pump control relay?

 

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According to one diagram that I have that is the L wire, for Lamp.  It supplies power to the alternator windings.  That would explain your problem.  Now you just have to find out why it doesn't have power.

 

Nissan made things complicated in 1978 with lots of extra relays and gizmos.  I think that the best you can do is to follow that wire back.  Looks like it gets power through a"check relay" (maybe your e-brake warning light) and also the Charge lamp.  The Charge lamp in the meter should light up when the key is on.

 

The colors aren't right in my copy of the 78 FSM but it shows the various connectors.  Maybe you just lost a connection.

 

Edit - looks like they only mislabeled the color, WB, right at the plug.  It's back to "L" (blue) farther down the circuit.  It does indicate a splice to a yellow wire along the way.  Nissan used a crimp on to exposed wire to create branches.  Likely a stressed point, susceptible to bending and fatigue.  

 

image.thumb.png.e860bdb44b3584c7dbe3e877f35fe034.png

image.png.256df046e68975ab77f36dc069e5aa44.png

 

Edited by NewZed
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16 hours ago, NewZed said:

According to one diagram that I have that is the L wire, for Lamp.  It supplies power to the alternator windings.  That would explain your problem.  Now you just have to find out why it doesn't have power.

 

Nissan made things complicated in 1978 with lots of extra relays and gizmos.  I think that the best you can do is to follow that wire back.  Looks like it gets power through a"check relay" (maybe your e-brake warning light) and also the Charge lamp.  The Charge lamp in the meter should light up when the key is on.

 

The colors aren't right in my copy of the 78 FSM but it shows the various connectors.  Maybe you just lost a connection.

 

Edit - looks like they only mislabeled the color, WB, right at the plug.  It's back to "L" (blue) farther down the circuit.  It does indicate a splice to a yellow wire along the way.  Nissan used a crimp on to exposed wire to create branches.  Likely a stressed point, susceptible to bending and fatigue.  

 

Hmm, I have been using a diagram for the whole car which shows things slightly different than that one. Question about the Bulb Check Relay...if that wasn't getting power from the fuse block, would that trigger the brake warning light on the speedometer? If so then the fuse makes the most sense as the cause of the problem, however visually the fuse looks fine. Going to try and change it anyway just to rule it out.

 

34 minutes ago, Sam280Z said:

Is the charge warning light coming on in the voltmeter gauge? the alternator will not charge if that bulb is burnt-out.

 

That's a likely culprit too as I had that gauge removed to change the main light to LED. I don't remember if I switched the charge light to LED or if it was a different size bulb. Unfortunately I don't think I will have time to remove the dash to get to it before I leave town for a week so that will have to wait if the fuse thing doesn't work which I kind of don't think it will based on the info below.

 

SIDE NOTE:

The whole car wiring diagram I have been staring at for hours shows the charging system wired a little differently than the diagram posted in this thread. The broken down diagram shows the whole circuit running off of one fuse while the whole car diagram shows it running off of two fuses (3rd + 4th from top on the Left). It shows the "G" wire coming off of the 3rd fuse down whereas the broken down diagram shows it coming off of the 4th. The whole car also shows the many other things that are powered by those two fuses, most of which work which kind of debunks the fuse theory. BUT the interesting thing is that all of my current problem areas with the car, all problems that started at the same time, can be traced back to those two fuses: Alternator not charging, e-brake warning light on speedo constantly lit, tach not reading RPMs, charge light on volt gauge doesn't work.

 

 

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I was going to mention what Sam280Z said about the Charge light.  But the diagram shows a parallel circuit with the check relay so that wouldn't be a problem IF the diagram is correct. Current through the check relay solenoid would supply the L circuit and the bulb circuit would not be necessary.

 

Now that you've mentioned all of the other problems, it seems more likely that it could be the cause and the diagram is not correct.  

 

Good luck.  At least you know that it's power to the L wire that is the problem.  

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2 hours ago, NewZed said:

I was going to mention what Sam280Z said about the Charge light.  But the diagram shows a parallel circuit with the check relay so that wouldn't be a problem IF the diagram is correct. Current through the check relay solenoid would supply the L circuit and the bulb circuit would not be necessary.

 

Now that you've mentioned all of the other problems, it seems more likely that it could be the cause and the diagram is not correct.  

 

Good luck.  At least you know that it's power to the L wire that is the problem.  

 

Yeah it's a starting point at least!

 

Side note. Replaced both of the fuses and as expected no change. They were good to begin with. The rest will have to wait a week until I get home and have some time to take the dash out and get to that volt gauge.

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  • 2 weeks later...

So I finally got back around to trying to tackle this issue again and unfortunately, no luck.

 

I took the entire dash out, took out the LED bulb I had swapped into the CHG light. Replaced it with a standard bulb. Ensure the wiring had good contact to/from the bulb and un-loomed and inspected the entire dash wiring harness. Everything on the dash end looks fine visually. Car still isn't charging, the CHG light still doesn't come on, the tach still doesn't work, and the e-brake light is still permanently lit.

 

So if we can eliminate any issues before the fuse panel and eliminate any issues behind the dash...what's next? 

 

Next on my hit list I think is the Brake Warning Check Relay. Anyone know where on the car that is located? Is that the relay under the passenger seat?

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Do you not have a hand held meter?  To use for measuring voltage?

 

When I posted the wiring diagrams I thought that you would see the circuits and check those.  Didn't know you'd remove the dash to change the bulb first.

 

Anyway, the diagram shows that power to the check relay and the charge lamp comes from a single fuse.  You might check that one. 10 amps, 4th down on the left side.  Edit - I see that you said the fuses look fine.  But you should be using your hand held meter or test light to confirm voltage, on both sides of the fuse.  If there's no voltage at the fuse, follow the circuit backward.  All the way to the fusible link.

 

The location of the relays is in the Body Electrical chapter.

 

image.png.1b1f5e0f2fbb4ca80ae45849f739fb2a.png

 

Edited by NewZed
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I did check voltage into and out of that fuse and they are both good. Ignition relay is also good. Everything worked fine before I stripped out the entire interior, wiring harness and all, to clean and rebuild it and the problems started immediately after it was put back together so it has to be something I messed up. Something missing a ground or hooked up wrong, or maybe I dropped a relay and broke it or something I am not sure but I feel it would be too much of a coincidence for something to just go bad naturally while the work was being done. That's why I removed the dash because one of the changes I made from factory was swapping all the bulbs to LED, including the CHG light. So I was hoping that was the issue. Plus pulling the dash isn't that hard and I wanted to put an eyeball on everything back there for peace of mind. Changed the CHG bulb back to stock, verified it had good contact. Wiring all looked great, everything appeared to be hooked up properly, no loose connections, etc. I don't think it was anything in the engine bay as none of that was touched and I am more confused by the wiring diagrams than anything else so I am attacking components first. I am REALLY hoping its the Brake Warning Lamp Relay that's under the passenger seat. That was removed and re-installed during the interior job. I don't know if it makes much sense as I am not proficient in reading wiring diagrams but I know that I can at least trace the wires from this relay to each thing that isn't working properly.

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You're not really grasping the basics of electrical circuit troubleshooting.  There is a path that the electricity follows.  Use your meter and follow that path until you find that point that has no electricity.  You don't have to hope or guess.  It will be yes-yes-yes--no as you check the critical spots on the path.  You probably left a connector unplugged, or mixed two up.  The shape of the connector matches what the diagram shows.  The tachometer diagram shows the position of the connector in the relay panel.  Poke-read-poke-read-poke-read....

 

Edit - the case of the alternator needs a good ground.  It should ground through the mounting points but there is also a dedicated ground terminal, the "E" post.  Check the ground.  With your meter.

 

image.thumb.png.b97b1f532e58e3d6976ba1fc6fe2f475.png

Edited by NewZed
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58 minutes ago, NewZed said:

You're not really grasping the basics of electrical circuit troubleshooting.

 

I'll be the first to admit that! 

 

58 minutes ago, NewZed said:

There is a path that the electricity follows.  Use your meter and follow that path until you find that point that has no electricity.  You don't have to hope or guess.  It will be yes-yes-yes--no as you check the critical spots on the path.  You probably left a connector unplugged, or mixed two up.  The shape of the connector matches what the diagram shows.  The tachometer diagram shows the position of the connector in the relay panel.  Poke-read-poke-read-poke-read....

 

Understood. I just get a little confused on the path after it starts splitting up and going through the gauges and relays. I am likely just overthinking it and second guessing myself.

 

58 minutes ago, NewZed said:

Edit - the case of the alternator needs a good ground.  It should ground through the mounting points but there is also a dedicated ground terminal, the "E" post.  Check the ground.  With your meter.

 

Alternator ground is good.  Thanks for all your help by the way! I appreciate your patience.

Edited by TheWeekendWagon
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Man some things I just have the hardest time grasping. Math and electrical systems are my top 2. I tried to do my own research on relays so I can figure out how to wire in a new one but I have no confidence in my understanding. Sorry for the simple questions.

 

The way I understand a relay works is the coil is energized by a triggered power source on one end and ground on the other. Why then does the wiring diagram look like this?

 

44594891340_8a8115394c_c.jpg

 

It looks to me as though the coil is not directly grounded. The green wire (G) comes from the fuse panel so that's triggered power in by the ignition as the switch. The blue wire (L) is the one that goes to the alternator...the wire that isn't getting power. Does it ground through the alternator? The green/yellow wire (GY) runs through the e-brake switch, the light on the dash, and the fluid level switch. The black (B) goes to ground. 

 

Am I understanding this correctly? So when the ignition turns on power is sent through the coil to the alternator where it eventually grounds out activating the coil in the relay. The coil in the relay is used to trigger grounding out the GY wire. So, if the coil is fried in the relay power isn't going through to the alternator and it isn't being grounded so there's no triggering the relay. That doesn't ground out the GY circuit and the light on the dash stays on. Bob's your uncle that's my problem!? Or am I way off? haha.

 

If I am correct then I could wire in a standard relay as follows...

86 - G

85 - L

30 - GY

87 - B

 

I just want to run it by you all before I catch something on fire.

Edited by TheWeekendWagon
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Seems right.  30 and 87 are the power for the device that is being controlled, B and GY.  85 and 86 are the circuit that does the controlling, G and L.

 

Yes, L would ground through the alternator.  So that could be your missing L wire power, although there's supposed to be a second circuit, through the charge lamp.  I'm not sure that diagram is right though, as you thought.  Seems off.  What bulb is being checked?  The bulb check relay could be your whole problem.

 

Good luck.

 

image.png.f6bf7eb379e582ad7dadf91db733d2e1.png

 

 

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7 minutes ago, NewZed said:

Seems right.  30 and 87 are the power for the device that is being controlled, B and GY.  85 and 86 are the circuit that does the controlling, G and L.

 

Yes, L would ground through the alternator.  So that could be your missing L wire power, although there's supposed to be a second circuit, through the charge lamp.  I'm not sure that diagram is right though, as you thought.  Seems off.  What bulb is being checked?  The bulb check relay could be your whole problem.

 

Good luck.

 

image.png.f6bf7eb379e582ad7dadf91db733d2e1.png

 

 

 

The bulb being checked is the brake light on the speedo that is currently constantly lit. I am really hoping this relay is the whole problem, but I at least think it will fix the light in the dash. When it's not energized the light is not grounded out and it stays on. Its also tied to the e-brake handle which when depressed completes the connection to the relay to ground it out. When you pull the e-brake up, the connection is broken and the light comes on. Gonna try wiring in the new relay in the morning and if all goes well drive around without the passenger seat for a bit to make sure it doesn't catch on fire which looks like what happened to the old one.

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That makes sense.  I just checked my 76 diagram and it has those two sources for the L pin power at the alt also.  Didn't realize that.  Thought it was just the Charge lamp.

 

Still doesn't explain why the Lamp (Charge light) in the meter doesn't power the L pin at your alternator.  You might find that things work but you'll be missing the Charge light.  One thing at time.  Good luck.

 

The burnt relay isn't too surprising.  I've found one burnt one on my car, plus one that was a pile of rust inside.

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