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

[NocturnalEmber]

Hey there everyone.  I'm currently trying to iron out some issues with my car, and if anyone would be kind enough to lend me their advice and insight, I would be very grateful! Huge thanks to @SteveJ for encouraging me to post here!

I've got a new to me 1978 280Z (five speed manual) that I am trying to get back on the road. Body wise it seems to be in great shape and overall it seems to be mechanically complete.  However, I am having some issues with the interior gauges not functioning. Here is the state of that: 

*No functionality on any gauge except volt meter - Oil, water, fuel, tach, clock. - None of them are functional.

*No functionality of turn signals (but hazards work.)

*No functionality of blower motor

*Rear defrogger switch appears to illuminate.

*All fuses are okay and tested (in the fuse box at passenger kick panel.) 

*Headlight and wiper functionality are fine, but the interior backlights do not illuminate; **unless a wire is wiggled.** I've traced this down to a red power wire at its connection to the PCB on the headlight switch. Wiggling this wire where it connects to the pcb will make the backlights come on (when the switch is in the position for them to turn on.)

I've looked at the FSM and electrical wiring diagrams, and from what I can tell (though I may be wrong), every single thing that is non functional that I've listed above goes through the ignition relay, so I'm leaning towards it being the possible culprit. Again, the only interior gauge that works is the volt meter, and to my knowledge it doesn't go through the ignition relay. With the key on, sometimes the car will spring to life and things like the seat belt warning will come on, but it's only done that maybe once or twice.

I placed my hand on the Ignition relay when I cycled the key from off to on, and I can feel something, but I don't know if its really working or if its just stuck and trying to work. It looks fine on the outside, and the ground wire is tight.

The wiring looks original and untouched from what I can tell. I don't see any visible splicing or cutting or anything that does not look out of place in relation to what is around it (example: No five year old electrical tape on an obviously 45 year old car.)  I've looked basically anywhere I can crawl under and into to look at the wiring harness, and nothing looks damaged that is readily visible.

 

Does anyone have any idea where I could start with this one?  I'm leaning towards the ignition relay.

 

Starting and running wise, the car will start and run when cold. However, when warm it will not restart.

The fuel pump will prime and activate when ignition is in the start position and the car will start and run, but giving it throttle or trying to restart it in warm is an exercise in futility. I've checked all the grounds in the engine bay and they appear fine.

What I've replaced:

*New battery

*New plugs

*New wires

*New coil

*New distributor cap

*New fuel injectors with seals and o rings x6

*New fuel filter

*new soft lines from tank to pump (3/8") and FI rated hoses from pump to its next connection, as well as both the feed and return lines in the engine bay connecting to the fuel rail (5/16".)

*Added Fram G3 inline filter in between tank feed line and pump inlet

 

In terms of this issue, it was suggested I look at the coolant temp sensor due to it being an issue of restarting when hot.

 

Thank you for the help everyone, I really appreciate it!

[Zed Head]

The pinout to the relay is shown in the wiring diagram.  And you can easily pry the four tabs up and take the cover off.  Don't overlook that it grounds through the mounting points.  Looks like they might have added a wire in 78, I don't think my 76 had that.

[siteunseen]

I had bought a bad "new reman" alternator for mine that back charged? and popped all my glass fuses. DOA, nothing worked. I asked the guys on here and they suggested checking the fuses. That was the dead giveaway. They were all smoked. Went to get another alternator and had it tested before I left with it. No problems since then.

[SteveJ]

2 hours ago, Zed Head said:

The pinout to the relay is shown in the wiring diagram.  And you can easily pry the four tabs up and take the cover off.  Don't overlook that it grounds through the mounting points.  Looks like they might have added a wire in 78, I don't think my 76 had that.

Actually, there wasn't a wire added to the 78. The ignition relays are the same.

[Zed Head]

Yes, I looked at the 76 diagram and it shows the same thing.  What's funny is that the ZX's did have a terminal and a dedicated ground wire so the drawing does match a ZX.  Weird.  It was a spade terminal though, not a threaded stud.  I picked up a spare from a ZX just in case.  In the ZX's they're behind the glove box.

Here's a listing and a picture of 78 relay.  You can see the four places to bend to get the cover off.  I called them tbas but they're really more like crimps.  A pair of straight jaw pliers and four squeezes and it will pop right off.  Might be a ground wire connected inside though so be careful, if you get that far.

https://www.autopartone.com/products/75-76-77-78-datsun-280z-oem-ignition-relay-25230-89958

[Zed Head]

Here's a ZX relay just to fill the thread out.  Maybe it's just two years.

https://www.autopartone.com/products/79-80-datsun-280zx-oem-relay-25230-w0500

[Reptoid Overlords]

Definitely not the cure for the dash components, but in case your problem is a compound problem, I recently went through a no start when hot problem with my '91 civic.  It ended up being that the spade connector to the starter solenoid had vibrated loose enough to make contact when cold, but as heat built up in the engine bay, I guess it would expand enough to not make contact.  Or something to that effect.  

I replaced it with a better spade connector and it fired right up hot or cold.  Zed Head, Steve J and others commented on this recent thread where the OP had an intermittent no start situation.  

Picture of spade connector from that thread:

Edited August 26, 2023 by Reptoid Overlords

[NocturnalEmber]

1 hour ago, SteveJ said:

Actually, there wasn't a wire added to the 78. The ignition relays are the same.

I yield to your expertise, but my relay has an extra ground wire coming off of it that is held down with one screw. I'll run out to the car and attempt to get a clear photo of it. I could very well be an idiot, but I'm 99% sure the ground wire is there, and the part number "25230-89958" is printed on the side. What would cause mine to have the extra ground wire if it wasn't added in 78? It looks factory?  Will update when I can get a picture of it (likely within the hour)

 

EDIT: went and looked, no ground wire coming off of it, but there is one bolter to it's bracket (which was the source of my confusion.) Photo in next post.

45 minutes ago, Reptoid Overlords said:

Definitely not the cure for the dash components, but in case your problem is a compound problem, I recently went through a no start when hot problem with my '91 civic.  It ended up being that the spade connector to the starter solenoid had vibrated loose enough to make contact when cold, but as heat built up in the engine bay, I guess it would expand enough to not make contact.  Or something to that effect.  

I replaced it with a better spade connector and it fired right up hot or cold.  Zed Head, Steve J and others commented on this recent thread where the OP had an intermittent no start situation.  

Picture of spade connector from that thread:

The starter is brand new (I actually forgot to mention that in my original post, my mistake.) The car will crank when warm or hot, it just won't start when hot. The fuel pump activates when the key is turned to start, as does the starter when the spade connector is connected.

Edited August 26, 2023 by NocturnalEmber

[Yarb]

What is your fuel pressure between the filter and fuel rail? I know it might sound off base but that needs to be clarified IMO.

[NocturnalEmber]

I just went out and took a photo of the ignition relay in the car, there is a tiny ground wire that comes off the car side of the harness and bolts to the bracket of the Ignition relay, which was the source of my confusion.

The ground wire, however, does not seem to be coming from the ignition relay itself.

Picture of the ground wire bolted to the bracket below, and if the relay itself.

 

Picture of the relay; the ground wire I was talking about is clearly visible with it's bullet connector. Goes into the car harness, doesn't look like any ground wire is coming out of this relay, chalk that up to my ignorance!

Anyway, it looks to be in good shape but I'm guessing it may likely be the culprit for what is not functioning vs what is (basically only the voltmeter.)

Edited August 26, 2023 by NocturnalEmber

[NocturnalEmber]

5 minutes ago, Yarb said:

What is your fuel pressure between the filter and fuel rail? I know it might sound off base but that needs to be clarified IMO.

I tested it when I installed the new filter and lines, and I believe it was 36~ when running.

[SteveJ]

3 hours ago, NocturnalEmber said:

Hey there everyone.  I'm currently trying to iron out some issues with my car, and if anyone would be kind enough to lend me their advice and insight, I would be very grateful! Huge thanks to @SteveJ for encouraging me to post here!

I've got a new to me 1978 280Z (five speed manual) that I am trying to get back on the road. Body wise it seems to be in great shape and overall it seems to be mechanically complete.  However, I am having some issues with the interior gauges not functioning. Here is the state of that: 

*No functionality on any gauge except volt meter - Oil, water, fuel, tach, clock. - None of them are functional.

*No functionality of turn signals (but hazards work.)

*No functionality of blower motor

*Rear defrogger switch appears to illuminate.

*All fuses are okay and tested (in the fuse box at passenger kick panel.) 

*Headlight and wiper functionality are fine, but the interior backlights do not illuminate; **unless a wire is wiggled.** I've traced this down to a red power wire at its connection to the PCB on the headlight switch. Wiggling this wire where it connects to the pcb will make the backlights come on (when the switch is in the position for them to turn on.)

I've looked at the FSM and electrical wiring diagrams, and from what I can tell (though I may be wrong), every single thing that is non functional that I've listed above goes through the ignition relay, so I'm leaning towards it being the possible culprit. Again, the only interior gauge that works is the volt meter, and to my knowledge it doesn't go through the ignition relay. With the key on, sometimes the car will spring to life and things like the seat belt warning will come on, but it's only done that maybe once or twice.

I placed my hand on the Ignition relay when I cycled the key from off to on, and I can feel something, but I don't know if its really working or if its just stuck and trying to work. It looks fine on the outside, and the ground wire is tight.

The wiring looks original and untouched from what I can tell. I don't see any visible splicing or cutting or anything that does not look out of place in relation to what is around it (example: No five year old electrical tape on an obviously 45 year old car.)  I've looked basically anywhere I can crawl under and into to look at the wiring harness, and nothing looks damaged that is readily visible.

 

Does anyone have any idea where I could start with this one?  I'm leaning towards the ignition relay.

 

Starting and running wise, the car will start and run when cold. However, when warm it will not restart.

The fuel pump will prime and activate when ignition is in the start position and the car will start and run, but giving it throttle or trying to restart it in warm is an exercise in futility. I've checked all the grounds in the engine bay and they appear fine.

What I've replaced:

*New battery

*New plugs

*New wires

*New coil

*New distributor cap

*New fuel injectors with seals and o rings x6

*New fuel filter

*new soft lines from tank to pump (3/8") and FI rated hoses from pump to its next connection, as well as both the feed and return lines in the engine bay connecting to the fuel rail (5/16".)

*Added Fram G3 inline filter in between tank feed line and pump inlet

 

In terms of this issue, it was suggested I look at the coolant temp sensor due to it being an issue of restarting when hot.

 

Thank you for the help everyone, I really appreciate it!

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.