78 280z turns off with turn signal/reverse lights

[Usain_Boat]

Daily update: took apart every connector I could find that might be part of the problem and cleaned them very well including the leads for all the relays, the fusible link terminals and other things. After doing this I plugged everything up fired it up and shifted into reverse which killed it again Though this time, I could shift in and out of reverse and hear some relay (wasn't able to track it down) click on and off while the dash lights (batter charge and brake indicator) turned on and off with shifting into reverse. After about 10 times the car quit doing it so I was not able to test anymore.

 

Edited July 29, 2019 by Usain_Boat
Last sentence had typos

[SteveJ]

Okay, here is an explanation of the fuel pump control relay and fuel pump relay

78 Fuel Pump Relay Notes
There are two relays
1. Fuel Pump Control Relay
2. Fuel Pump Relay

Fuel Pump Control Relay:
Positive coil voltage comes from the white/black wire (Origin is the Ignition Relay)
One coil is grounded through Alternator (blue wire).
The other coil is grounded through the oil pressure switch (yellow/black).
The relay has form C contacts.
A contact puts wiper (white/black) in contact with power from ignition relay.
B contact puts wiper in contact with power from engine cranking (black/yellow wire).
(Note: This is opposite of how it is drawn in the factory wiring diagram, but how it is drawn does not make sense.)
The wiper provides coil power to the Fuel Pump Relay.

Fuel Pump Relay:
Positive coil voltage comes from the white/black wire from the Fuel Pump Control Relay wiper.
Form A contacts connect two green/blue wires. One side comes from a fusible link. The other side goes to the fuel pump.

Theory of operation:
When cranking the engine, within the Fuel Pump Control Relay, the second white/black wire mentioned above is connected to the start position on the ignition switch. This energizes the Fuel Pump Relay and powers the fuel pump.
If the engine starts, the key is released to the ON position, and the first white/black wire is energized from the ignition relay. The blue wire is grounded through the alternator and the coil is energized within the Fuel Pump Control Relay. This closes a set of contacts within the Fuel Pump Control Relay that allows the second coil to energize, provided there is sufficient oil pressure. With the second coil energized, the power from the ignition relay is providing power to energize the coil on the fuel pump relay.

How this applies to your problem:

The odds are that the voltage is dropping on the white/black wire coming off the ignition relay.

List of components fed from the white/black wire from the ignition relay:
Fuel Pump Control Relay
Electronic Fuel Injection Main Relay
Flasher fuse (Green wire)
Fuel Gauge fuse (Blue wire)

The loads off the Flasher fuse:
Brake Warning Lamp Check Relay
Turn signals
Seat Belt Warning Timer Unit
Fuel Level Warning Lamp
Reverse Lights

The loads off the Fuel Gauge fuse:
Fuel Gauge
Water Temp/Oil Pressure Gauge
Tachometer

Process of Elimination:

There are several components here that we can definitely cross off as problematic: Fuel Pump Control Relay, EFI Main Relay, Seat Belt Warning Timer Unit, Fuel Level Warning Lamp, Fuel Gauge, Water Temp/Oil Pressure Gauge, Tachometer.

So IIRC, you said that the car would die when using turn signals or putting the car into reverse. Those are BOTH powered off the flasher fuse in the fusebox, and the flasher fuse gets its power via the white/black wire from the ignition relay.

There is even a common point for these two circuits that initiate the problem: the right rear taillight assembly.

Here is a simple test. Disconnect the wiring harness going to the right rear taillight assembly. Start the car and try to put it into reverse. If it does not die, try turning on the right turn signal. If it does not die, you have confirmed that the issue is at the right rear taillight assembly. You may have to take off the plastic panel to access the connector.

[SteveJ]

Oh, since we would expect the flasher fuse to blow, check the rating on the fuse to make sure it is only 10A.

[Usain_Boat]

18 minutes ago, SteveJ said:

Oh, since we would expect the flasher fuse to blow, check the rating on the fuse to make sure it is only 10A.

I've gone through them and it is 10A that's part of what's baffling me.

[Usain_Boat]

Also the problem is very intermittent and doesn't want to happen right now so I'll have to wait for it to act back up.

[SteveJ]

FYI to the reading public, @Usain_Boat and I have talked on the phone. He is going to examine the body wiring harness for signs of damage. The cutting off may be happening with the left turn signal, too. The common path is through the body wiring harness. Fortunately, the interior panels are off so he can trace it more thoroughly.

[Usain_Boat]

Took a look at the rear of the harness this morning and I don't see anything suspicious. The place where the electrical tape is where it was already peeling off so I peeled it back further to look. Attached are pictures

[gwri8]

Don't forget to inspect/clean the sockets while you are there.

[wal280z]

5 hours ago, Usain_Boat said:

Took a look at the rear of the harness this morning and I don't see anything suspicious. The place where the electrical tape is where it was already peeling off so I peeled it back further to look. Attached are pictures

Is it me or does this taillight harness appear to be spliced? (black heat shrink) 

[Usain_Boat]

This evening I disconnected the reverse switch to isolate that and it died with the left turn signal. I could hear the ignition relay clicking on and off with the blinkers. At this point I know of two instances where the left turn signal has killed the car not sure on the right turn signal.

[wal280z]

On 7/28/2019 at 2:34 PM, Usain_Boat said:

Digging deeper I do remember some splices in for the connections to the fusible link that I thought I fixed from the PO. When I got the car there were heat shrink crimps where the plastic was cracked and gone so I took them off and redid them. The fusible link in question (I believe it's the one closest to the engine in the front) has some green corrosion within the crimp and I also didn't get all the strands into the crimp. If I was to cut all of this out and redo it what gauge wire should it be? It looks heavier than the 14 gauge I have and is getting pretty short from whatever the PO did.

Question - Did YOU do the splicing, or just repair what was already done?

Did you OHM the connections prior to re-splicing? Wondering if one of those connections got switcher-ro'd.

There was a recent thread about fusible links created by @EuroDat and all evidence has pointed to the Factory wiring diagrams being incorrect from 1976-1978 - the front most fusible link holder being suspect.

[Usain_Boat]

16 minutes ago, wal280z said:

Question - Did YOU do the splicing, or just repair what was already done?

Did you OHM the connections prior to re-splicing? Wondering if one of those connections got switcher-ro'd.

There was a recent thread about fusible links created by @EuroDat and all evidence has pointed to the Factory wiring diagrams being incorrect from 1976-1978 - the front most fusible link holder being suspect.

The splices were already done by the PO, I just replaced the crimps. I didn't check that they went to the correct places though I did notice Saturday that the front and rear blocks are wrong in the wiring diagram for 78.

Edited July 30, 2019 by Usain_Boat
Answered another question