78 280z turns off with turn signal/reverse lights

[Usain_Boat]

Just tested the ignition switch as the FSM details and it has continuity across the correct pins at the correct positions.

[Patcon]

@SteveJ

[gwri8]

Also check for any wobble in the pins.  I just had one that tested ok but one of the pins was loose and created an intermittent problem.

[SteveJ]

First verify the battery is good. A bad battery or charging system with the accompanying voltage drop could account for some of the issues. Get the battery load tested. Don't try running the car with a low battery. You can damage things that way. By the way, what is the battery voltage right now? Check with a meter, not the voltage gauge on the dash. I'll trust a 40 year old Simpson meter. I'm not sure I would completely rely on the 40 year old voltage gauge.

Verify the presence/absence of spark with an inline spark tester (https://www.harborfreight.com/90-in-line-spark-checker-63593.html). Have someone crank the ignition while you watch for spark. Do this in a relatively dark setting.

Again, look for wiring modifications from a previous owner.

Search on this site. I know I have provided diagnostics for the 78 fuel pump relay and even described how to bypass the relay for testing.

[Usain_Boat]

@SteveJ here are some pictures if you want more specific ones I can take more. Also the battery is at 12.97V

Edited July 27, 2019 by Usain_Boat
Misspelled if and added battery info

[Usain_Boat]

It runs again... I cleaned all the contacts again for peace of mind before dinner, plugged it all back in and nothing. Then after dinner I started tracing power through the relays that turn on the fuel pump since i didn't have power there and I had power through the fuel pump control relay to the fuel pump relay and too the pump. I am very confused as I did nothing in between the two times and tested no voltage to the fuel pump before dinner and I have power after dinner. A possible clue is as I said I had no dash lights or gauges earlier, when I went to try and start it after testing I had dash lights and gauges again.  After all I've been through with this car I highly doubt anything is actually fixed but I am confused as to what the problem could be.

[Usain_Boat]

Sorry if I'm posting too much tonight but I just want to give as much information from my side as possible. After the car decided to turn back on It was back to the title of the thread, turning off when shifting into reverse. I stuck my probe of the multi meter into the plug at the very beginning of the fuel pump +, stuck the other to ground, turned on the car, took off the e-brake, braked, clutched in, and shifted into reverse. I then watched the voltage to the pump drop to zero and the car turned off. I turned it off and tried to turn it back on but no dice. I then clutched in with the key in on, heard a click, dash lights and gauges came back on and then it would run again. I tried to replicate the turning off in reverse probing other wires but I wouldn't shut off again.

[SteveJ]

You're not posting too much. You are providing detailed observations. From this I can look at the wiring diagram and try to find some things for you to look at.

Did you strip off the wrapping around the wiring harness, or was that the work of a previous owner?

From picture 1, I can't tell if those are factory splices in the background.

From picture 3, is that the end of a wire that has been cut?

From my previous comment, it sounds like someone was trying to fix something and may have introduced a short. Just wild speculation, but it may be that the power for the second fuel pump relay coil or the fuel pump itself gets shorted out with the reverse switch. The car dies (and the damaged circuit loses power) before a fuse or fusible link is blown.

If you can get under the car easily and access the reverse switch on the transmission, take it out and see if that resolves the car dying when going into reverse. Also while you're under the car, see if either side of the reverse switch has continuity to ground.

[grannyknot]

It sounds like the reverse switch is shorting something, there are two solid green wires from the reverse switch, one goes straight to the reverse lights the other goes to the voltage gauge charge light, the low fuel warning light, the flasher fuse in the main fuse box and the hazard switch. ALL of the connectors in those two lines should be pulled apart, inspected and cleaned to eliminate them as a cause.

I'm using the wiring diagram for a 77/ 280z

Edited July 27, 2019 by grannyknot

[Usain_Boat]

@SteveJ the insulation being taken off is me looking for the short and the wire in #3 is not broken here is a close up

[Usain_Boat]

I got the front end on ramps and took a look at the reverse switch leads. The two female bullet connectors on the harness were very dirty so I cleaned them. One is continuous to ground and the other isn't. On the switch itself both male leads aren't continuous to ground. I'm not sure if it's advisable but I have continued removing the outer insulation on the harness to follow the reverse wires. 

[Usain_Boat]

Here are more pictures of the wiring harness undressed from where the reverse switch wires leave to the fuse box. Nothing looks "fixed" to me.