78 280z turns off with turn signal/reverse lights

[Usain_Boat]

So I got the car to die this morning and just tried to follow the power back. The Ignition relay is still on but i have like 60mV across the whole line even back to its fusible link. I decided to follow most of the circuit and take resistance measurements which are as follows. Fusible link to ignition relay: 0 Ohms

Across ignition relay: 0 Ohms

Ignition relay to fuse block: 5 Ohms to the fuse and 7 Ohms to the green wire side of the flasher fuse.

Ignition relay to C4: 0 Ohms

Ignition relay to fuel pump control relay: 4.5 Ohms

Fuel pump relay to Fuel pump control relay: .1 Ohms

To be clear, this is following the White/Red wire from the fusible link to the ignition relay where it leaves as a White/Black wire. 

Another observation I made through this process was the ignition relay got noticeably warm while there was 60mV on the circuits above. Could my ignition relay have an internal short that is causing this? Because if I understand the ignition relay shouldn't have enough resistance to get hot.

I also checked for power from the Black/White wire from the ignition switch and it is showing 12.8 V so the ignition relay should definitely be on.

[SteveJ]

15 minutes ago, Usain_Boat said:

So I got the car to die this morning and just tried to follow the power back. The Ignition relay is still on but i have like 60mV across the whole line even back to its fusible link. I decided to follow most of the circuit and take resistance measurements which are as follows. Fusible link to ignition relay: 0 Ohms

Ignition relay to fuse block: 5 Ohms to the fuse and 7 Ohms to the green wire side of the flasher fuse.

Ignition relay to fuel pump control relay: 4.5 Ohms

These numbers seem high to me. The resistance across wire runs should be very low. You may want to validate your readings. Keep in mind that the quality of the probe with the wire being measure can greatly affect your readings. Make sure you have very firm contact on each side of the circuit.

[Zed Head]

2 hours ago, Usain_Boat said:

Another observation I made through this process was the ignition relay got noticeably warm while there was 60mV on the circuits above. Could my ignition relay have an internal short that is causing this? Because if I understand the ignition relay shouldn't have enough resistance to get hot.

The 280Z's have the relay in a bad spot.  Gets wet if there's a leak.  They're easy to take apart, just bend the crimped lock tabs back and pull the cover off.

[Usain_Boat]

Well I went with a hunch and built a new ignition relay out of two 40 amp SPST relays like @SteveJ  (I believe) outlined on zcar.com and it still dies in reverse. I took the readings aforementioned by sticking the probes in the back of the connectors while it was dead so I could keep it in the state that kills the car. It is possible they aren't the best readings. If I was to take them again, what would be the best way? 

[Usain_Boat]

Just opened the ignition relay as best I could and Its not rusty inside, the ground is still attached and I would rather not break it so I wasn't able to open it all the way.

[Zed Head]

5 hours ago, Usain_Boat said:

So I got the car to die this morning and just tried to follow the power back.

It's not clear why the engine needs to be running for this problem to manifest itself.    Also not clear that the fuel pump power is the main reason the engine dies.  Seems more like you're losing all ignition relay power, not just fuel pump power.  Do other things shut down?  Radio, heater blower, windshield wipers, etc.  Those are accessory items but I think that they use the same supply line to the ignition relay.  Also, voltage to the coil should go away if it's an ignition relay problem.

Maybe connect a test light or two to your ignition relay's input and output then put it in and out of reverse and see if something different shows up.

And don't forget the Hazard switch.  It is the cause of many mysterious electrical problems.

[Usain_Boat]

Just now, Zed Head said:

It's not clear why the engine needs to be running for this problem to manifest itself.    Also not clear that the fuel pump power is the main reason the engine dies.  Seems more like you're losing all ignition relay power, not just fuel pump power.  Do other things shut down?  Radio, heater blower, windshield wipers, etc.  Those are accessory items but I think that they use the same supply line to the ignition relay.  Also, voltage to the coil should go away if it's an ignition relay problem.

Maybe connect a test light or two to your ignition relay's input and output then put it in and out of reverse and see if something different shows up.

And don't forget the Hazard switch.  It is the cause of many mysterious electrical problems.

I took apart and cleaned the hazard switch recently to get the turn signals work so what should I look for wrong there?

The power from the ignition switch to the ignition relay doesn't die, the Black/White wire at the relay still has 12.8 volts so that should have the coil energized and the relay still on. The problem is the voltage on the circuit that provides power to the flasher fuse, fuel pump control relay, and fuel pump relay loses power. This is the White/Black wire when it leaves the ignition relay. The Black/White wire that comes from the ignition switch has power at the relay, I'm not sure if it loses power in a shutdown event. I haven't tested anything else to be dead but next time I will test the wipers and blower.

[Zed Head]

9 minutes ago, Usain_Boat said:

The power from the ignition switch to the ignition relay doesn't die, the Black/White wire at the relay still has 12.8 volts so that should have the coil energized and the relay still on. The problem is the voltage on the circuit that provides power to the flasher fuse, fuel pump control relay, and fuel pump relay loses power. This is the White/Black wire when it leaves the ignition relay.

You just described a bad relay.  Not sure why your fabbed-up relay didn't work.  You're saying that the coil is energized but the switch is not transmitting power.

Be the relay.  Short across the circuit in the relay that you think is losing power.  If it fixes the problem then the relay is bad, either  the contacts are dirty or the solenoid isn't working.  If it doesn't fix the problem then you can move on from the relay.

[Usain_Boat]

23 minutes ago, Zed Head said:

You just described a bad relay.  Not sure why your fabbed-up relay didn't work.  You're saying that the coil is energized but the switch is not transmitting power. Be the relay.  Short across the circuit in the relay that you think is losing power.  If it fixes the problem then the relay is bad, either  the contacts are dirty or the solenoid isn't working.  If it doesn't fix the problem then you can move on from the relay.

So when I was testing while the car was dead, the relay had continuity across the contacts from the White/Red from the fusible link to the White/Black. Therefor the relay was working as intended I believe. The problem is that 60 mV on the circuit is not going to be enough to energize the fuel pump control or fuel pump relays that are on that wire. Also, the reverse lights are not on either since there is not enough voltage to run them. Through all of this the car will die once but as soon as you shift out of reverse and restart the car it won't do it again for a while.

[Zed Head]

Don't assume that continuity and low voltage mean the relay contacts are making good contact.  Sounds like you have a bad relay.  The test I described will show you if that's the case.

The measurements only get you so far, typically showing what's working correctly.  Your measurements have shown you that something is not right in the relay.  The next step is testing.

[Usain_Boat]

35 minutes ago, Zed Head said:

Don't assume that continuity and low voltage mean the relay contacts are making good contact.  Sounds like you have a bad relay.  The test I described will show you if that's the case.

The measurements only get you so far, typically showing what's working correctly.  Your measurements have shown you that something is not right in the relay.  The next step is testing.

Ok, I will keep testing with the ignition relay completely bypassed.

[Usain_Boat]

Engine still died with the ignition relay bypassed.