1978 280Z - Won't restart when hot, all interior gauges, fan motor, backlighting not working

[Zed Head]

It might help to restate the state of affairs.  One change seems to be that "won't start when hot" has morphed in to "runs funny after it starts".

[NocturnalEmber]

On 8/26/2023 at 7:04 PM, SteveJ said:

First let's go over the ignition relay and what it does. That way we can trace down the problems.

Note: The copy of the 78 diagram I have still shows the relay drawn incorrectly. I think I made the proper adjustments.

Color Code
L - Blue
B - Black
W - White
Y - Yellow
R - Red
G - Green

When there are two letters, the first is the main wire color, and the second is the stripe. B/W is black with white stripe.

So there are two coils in the ignition relay. One coil is energized by the key in ACC or ON. That comes in on the L/R wire. The set of contacts is connected to a W/R wire that traces back to the black fusible link. It goes out as the L/R wire

The other coil is energized by the key in ON, and that comes in on the B/W wire. The set of contacts associated with that coil is connected to a W/R wire from a different fusible link. It goes out as the W/B wire.

I traced out those wires coming off the relay.

L/W Wire   Fuse Box (ACC)   L/Y Air Con Blower Motor   AC Relay   Mag Valve Vac   L/R Wiper Wiper Power   Washer Pump   L Radio Radio Power   Antenna Sw   Rear Defogger       W/B Wire   Floor Sensor  Cal only Fuel Pump Not during cranking Inhibitor Sw AT only Fuse Box (IGN)   G Turn Signal Brake Warn Lamp   Turn Signal Power   Seat Belt Warn Tmr   Fuel Lvl Warn Lamp   Reverse Lights   L Gauges Cooling Fan Relay   Fuel Gauge   Water Temp Gauge   Oil Temp Gauge   Tachometer   Speedometer Unk Func Kickdown Sw AT only

 So many of your issues revolve around the ignition relay. Is it bad? Test with a voltmeter. Note: All of these measurements will require the black probe of the meter on a good ground.

1. Unplug the ignition relay.
2. Measure the voltage across the battery terminal. (This is battery voltage.)
3. Measure voltage to ground on each W/R wire. You should have battery voltage at each wire.
4. Put the key in ACC and measure voltage on the L/R wire. You should have battery voltage.
5. Put the key in ON and measure voltage on the L/R wire and the B/W wire. Both should have battery voltage.
6. If all those tests pass, turn the key to OFF and plug in the relay.
7. Put the key in ON and measure voltage at the RADIO fuse and the FUEL GAUGE fuse. Both should have battery voltage.

Let us know the results. Considering you said the wipers work, the ignition relay may not be the issue.

The dash lights are another issue. The red wire is for the headlights. The G/W and G/L wires are for the dash lights (and running lights including tail lights). 

Describe the non-start when warm in more detail. Does the car crank? It might be a vapor lock issue.

Do you have an AC car? Have you checked the blower resistor?

Is the turn signal flasher plugged in? It should be hiding under the dash on the driver's side. The hazard flasher is there, too. The turn signal flasher should have G/Y and W wires going to the connector. 

 

Whew, sorry for the delay @SteveJ, but I managed to crawl under the dash and get that testing done.

All of your tests were showing the correct voltage when I probed the respective wires into the harness with the key in the position you instructed. (I had the negative lead attached to the battery ground and probed with the positive.)

The radio fuse did give battery voltage, however the fuel gauge did not, it was 2.xx volts I want to say.  That was the only anomaly I want to say out of the testing.

 

Worth mentioning also before I began the tests I did put the key to ON to check and make sure the seatbelt warning and the brake light lit up on the dash, as I discovered and mentioned in one of my last posts that an apparent loose fusible link in the engine bay caused that to not happen.

 

I confirmed the seatbelt warning and brake light were illuminated on the dash, and then I turned the key off and began to test exactly as you instructed.

When I got to the point to turn the key to off and plug in the relay, I noticed when I plugged it in it made a connecting noise, but when I turned the key to on to measure the radio and fuel gauge fuses, the brake and seat belt light no longer illuminated.

I unplugged and plugged the relay in a few times and they have since came back to life

 

(is it possible to plug that relay in wrong? Like two pins over so only four are plugged in? I couldn't see when I was plugging it in as I did it by feel and not so much by sight so I wasn't sure if that was what was maybe what caused the brake and seatbelt light to not illuminate when I turned the key back on, and maybe I finally plugged it in right when those two lights started working again? But if it's impossible to plug that relay in wrong, maybe I'm just thinking too much into that)

 

At any rate, that aside, all tests were what you specified they should be, with the exception of voltage at the fuel gauge fuse, which was 1.935x

 

 

[SteveJ]

If the turn signal (flasher) fuse has voltage but the fuel gauge does not, the first question is "Did you check on both sides of the fuse?" 

If it has voltage on one side but not the other, I'm thinking it's a bad fuse. Otherwise, I would have to wonder if the fuse box is damaged. 

Here's the back side of the fuse box.  The inner columns are the supply. The outer columns are the wires that go out to the loads.

[NocturnalEmber]

17 minutes ago, SteveJ said:

If the turn signal (flasher) fuse has voltage but the fuel gauge does not, the first question is "Did you check on both sides of the fuse?" 

If it has voltage on one side but not the other, I'm thinking it's a bad fuse. Otherwise, I would have to wonder if the fuse box is damaged. 

Here's the back side of the fuse box.  The inner columns are the supply. The outer columns are the wires that go out to the loads.

@SteveJI only checked the radio and fuel gauge fuses, and on those I only checked the left side (closest to engine bay/front of car/firewall), I didn't check the right side for voltage for the radio or the fuel gauge fuse.

 

I did however use one of those fuse testers a few days ago that came with a pack of the same type of replacement fuses the car has (the factory ones) that I bought from Home Depot, and all of the fuses tested okay.

I didn't get a chance to look under the dash for the turn signal/hazard yet, but I will say the hazard switch and the hazards do work fine, turn signals do not.

The car is an AC car.

 

In terms of testing the relay,

 

Being that the voltage readings were all what you expected them to be, does that point to the ignition relay being bad?

 

[SteveJ]

16 minutes ago, NocturnalEmber said:

I did however use one of those fuse testers a few days ago that came with a pack of the same type of replacement fuses the car has (the factory ones) that I bought from Home Depot, and all of the fuses tested okay.

I didn't get a chance to look under the dash for the turn signal/hazard yet, but I will say the hazard switch and the hazards do work fine, turn signals do not.

The car is an AC car.

 

In terms of testing the relay,

 

Being that the voltage readings were all what you expected them to be, does that point to the ignition relay being bad?

 

Your testing shows a potential issue with the relay. Let's verify your testing.

1. Unplug the ignition relay.
2. Measure the voltage across the battery terminal. (This is battery voltage.)
3. Measure voltage to ground on each W/R wire. You should have battery voltage at each wire. I understand you had the same voltage on each wire as the battery.
4. Put the key in ACC and measure voltage on the L/R wire. You should have battery voltage.  I understand you had the same voltage here as the battery.
5. Put the key in ON and measure voltage on the L/R wire and the B/W wire. Both should have battery voltage. I understand you had the same voltage on each wire as the battery.
6. If all those tests pass, turn the key to OFF and plug in the relay.
7. Put the key in ON and measure voltage at the RADIO fuse and the FUEL GAUGE fuse. Both should have battery voltage. I understand that you had voltage at the RADIO fuse but not the FUEL GAUGE fuse. Furthermore, the turn signals did not work.

The fuel gauge and turn signals are powered by the same side of the relay. If you don't have voltage for the gauges at the fuse box (with a good fuse), I would expect the turn signals to be non-functional, too. I'm also betting that your reverse lights aren't coming on, either.

Let's look at what all powered by the W/B wire.

W/B Wire
Floor Sensor	Cal only
Fuel Pump	Not during cranking
Inhibitor Sw	AT only
Fuse Box (IGN)
G	Turn Signal
Brake Warn Lamp
Turn Signal Power
Seat Belt Warn Tmr
Fuel Lvl Warn Lamp
Reverse Lights
L	Gauges
Cooling Fan Relay
Fuel Gauge
Water Temp Gauge
Oil Temp Gauge
Tachometer
Speedometer	Unk Func
Kickdown Sw	AT only

Among other things if that relay is faulty, you could lose power to your fuel pump when the key is in ON. If the coil or contacts are breaking down, it would not surprise me if it was worse when the car is hot. Your engine could fire with the key in start and die shortly after when the key goes to ON due to the pump losing power.

As far as connecting the relay in the wrong direction, yes it's possible but difficult.

That edge should hit the piece of phenolic that is near the one row of pins on the relay. Also if the relay is attached to the relay panel, I would expect that you would have to twist the connector significantly to get it to be in the wrong orientation.

[NocturnalEmber]

50 minutes ago, SteveJ said:

Your testing shows a potential issue with the relay. Let's verify your testing.

1. Unplug the ignition relay.
2. Measure the voltage across the battery terminal. (This is battery voltage.)
3. Measure voltage to ground on each W/R wire. You should have battery voltage at each wire. I understand you had the same voltage on each wire as the battery.
4. Put the key in ACC and measure voltage on the L/R wire. You should have battery voltage.  I understand you had the same voltage here as the battery.
5. Put the key in ON and measure voltage on the L/R wire and the B/W wire. Both should have battery voltage. I understand you had the same voltage on each wire as the battery.
6. If all those tests pass, turn the key to OFF and plug in the relay.
7. Put the key in ON and measure voltage at the RADIO fuse and the FUEL GAUGE fuse. Both should have battery voltage. I understand that you had voltage at the RADIO fuse but not the FUEL GAUGE fuse. Furthermore, the turn signals did not work.

The fuel gauge and turn signals are powered by the same side of the relay. If you don't have voltage for the gauges at the fuse box (with a good fuse), I would expect the turn signals to be non-functional, too. I'm also betting that your reverse lights aren't coming on, either.

Let's look at what all powered by the W/B wire.

W/B Wire
Floor Sensor	Cal only
Fuel Pump	Not during cranking
Inhibitor Sw	AT only
Fuse Box (IGN)
G	Turn Signal
Brake Warn Lamp
Turn Signal Power
Seat Belt Warn Tmr
Fuel Lvl Warn Lamp
Reverse Lights
L	Gauges
Cooling Fan Relay
Fuel Gauge
Water Temp Gauge
Oil Temp Gauge
Tachometer
Speedometer	Unk Func
Kickdown Sw	AT only

Among other things if that relay is faulty, you could lose power to your fuel pump when the key is in ON. If the coil or contacts are breaking down, it would not surprise me if it was worse when the car is hot. Your engine could fire with the key in start and die shortly after when the key goes to ON due to the pump losing power.

As far as connecting the relay in the wrong direction, yes it's possible but difficult.

That edge should hit the piece of phenolic that is near the one row of pins on the relay. Also if the relay is attached to the relay panel, I would expect that you would have to twist the connector significantly to get it to be in the wrong orientation.

I appreciate the fine forensic analysis thus far @SteveJ ; it has been absolutely critical to assisting me with tracking this problem down.

I'm going to go crawl up under the dash and look/feel the relay again, It was indeed bolted to its home, and it went in and out of the plug with what minor strength I could muster with one hand curved like it was, there wasn't any forced contortion of the harness, etc to get it to plug in, it went in rather easy. So its entirely possible I was just over thinking things on the "did I plug it in one column of pins over" part. 

What you are saying about it losing power, that makes sense because the car would start when cold and the issue would creep up seemingly after it had idled for a short amount of time. 

What confuses me though, is why would the fuel gauge fuse have such low voltage? Just seems awkward for it to be so low.   On a side note - I have an ignition relay I can use as a test that I should be getting tomorrow, I believe it is known good working,so maybe that will shed some light on things.

Edited August 28, 2023 by NocturnalEmber

[SteveJ]

Without an opportunity to poke around the car, it's hard for me to pinpoint where the stray voltage is coming from. 

One other test to consider doing is to remove the connector from the relay and test resistance from the W/B wire at the connector to the fuel gauge fuse. If you see 0.3 ohms again, you know the wire is intact.

I've seen a lot of questionable repairs on wiring done by people with good intentions and bad knowledge. It's part of what makes distance diagnosis of electrical problems challenging. I can tell you exactly how it should work according to the factory manuals, but Bubba may have come up with a cheap fix at some time or other.

Then again, it could just be a bad ignition relay with corrosion building internal resistance, dropping the voltage.

[NocturnalEmber]

6 minutes ago, SteveJ said:

Without an opportunity to poke around the car, it's hard for me to pinpoint where the stray voltage is coming from. 

One other test to consider doing is to remove the connector from the relay and test resistance from the W/B wire at the connector to the fuel gauge fuse. If you see 0.3 ohms again, you know the wire is intact.

I've seen a lot of questionable repairs on wiring done by people with good intentions and bad knowledge. It's part of what makes distance diagnosis of electrical problems challenging. I can tell you exactly how it should work according to the factory manuals, but Bubba may have come up with a cheap fix at some time or other.

Then again, it could just be a bad ignition relay with corrosion building internal resistance, dropping the voltage.

That's one concern I had, was that there had been some kind of previous band-aid fixes, etc that I would have no prior knowledge of knowing.  Based on what I've seen in/around the car, the wiring looks untouched, but that is by no means a conclusive statement about the health of the harnesses.

I'll break out the multi meter again and test the W/B at the connector and at the fuel gauge fuse to see if the wire is intact'

[NocturnalEmber]

@SteveJ This actually just occurred to me, and I didn't think to mention it. When I turn the key to on, the "BRAKE" light on the instrument cluster is somewhat dim, it definitely does not look like it is illuminating fully...could this somehow tie in with corrosion on the relay building internal resistance ?

 

[SteveJ]

The brake warning lamp is on the same fuse as the turn signals. You already established you have low voltage at the fuel gauge fuse. You probably have the same low voltage at the turn signal fuse. The voltage is enough for the light to come on faintly, but it's not enough to trigger the flashers to flash or get the gauges to operate.

[Zed Head]

Jump the appropriate pins in the relay connector.  If the various lights are still dim then it's likely that the relay is fine.  That way you don't have to contort yourself to remove it.

There are a lot of connections on the brake warning lamp circuit.

[NocturnalEmber]

@SteveJ, I spent some time with the car this morning and I have something interesting to report.   I installed the four fusible links on the passengers side strut tower (mine were corroded at the wire connections, so I figured this would just be good maintenance at this point), and put the relay in. Upon turning the key to on, there didn't seem to be any difference whatsoever. I tried actuating the turn signals, and that just seemed like it put more load on the system and made the seatbelt light go off. 

I thought about what you had said regarding the fuses, and even though they had tested fine with the fuse tester, I pulled them all out and had a look. Turns out, the inside link of the fuses themselves had what looked like to me, oxidation and/or corrosion. I replaced the fuel pump level fuse, the turn signal fuse (basically what fuses you mentioned are in that fuse box that could be related to my issue). 

I turn the key to on, and the car came to life. Brake light was bright and shiny, fuel gauge went up to E (i only have four gallons in the tank assuming it was dry, so the sender might be off), the charge light illuminated on the volt meter, it seemed like the fuses themselves, while they tested good, were causing the issue.

I tried activating the turn signals via the stalk. Left turn signal just illuminates and stays on, the right one will work inside and outside the car.  I do not have reverse lights, and the AC blower motor doesn't work.

At this point I started the engine, and the tach was reading about 500~ RPMs. 

The engine was behaving exactly how it did before though, running rough and dying when I would attempt to give it throttle. It did however restart when I tried, but I have no idea if it restarting a few times was just coincidental luck.

One thing I did notice though, My thoughts are beginning to shift to the ignition switch as a possible culprit?

I switched the key to ON and pushed/wiggled the key (it stayed in the ON position during this, I didn't change positions of the key physically), and the seatbelt light lost power. I pushed and jiggled it again and the seatbelt light came back on. 

I'm glad the fuses turned out to be the cause as to why a lot of things weren't working, but with those seemingly fixed, is it possible the ignition switch is malfunctioning with how it is behaving?

I'm still stumped about the way the engine is running; It starts, but it doesn't run well and will die on throttle like I mentioned.