1975 280z Electrical Issue

[Barefootdan]

Hi all,

New here, with my 1975 Datsun 280z. I am in the process of getting it running. I was able to get a new battery and start testing electrical power. I had the headlights and tail lights working, then began to start cranking. It successfully cranked for about 10 seconds. I stopped and tried again, but this time no power. I lost power to all lights as well. I took out my multimeter and tested the fusible links first. I have power to the White wires (closest to the fender) in the box. But zero power to the White/Red terminals (closest to the engine). I checked my power to the starter and confirmed 12v. I even jumped the solenoid and was able to see the starter working this way. I am a bit stumped. I tested the White/Red from the alternator to the battery and have 0v. Is this my issue? Is there a connection between the White starter and White Red Alternator that is causing my issue?  

[Zed Head]

Might be that you fried a fusible link or that the terminal on the link lost its connection.  Clean up the ends, give them a little extra crimp, and see.  Check resistance through the links also.  Pretty common to lose connection though.  They're exposed and they corrode.

[Barefootdan]

The two fusible links have continuity through them, although one could be fried. My initial test was testing the terminals directly. I had 12v at the White (alternator and IGN relay) terminal, but none at the White/Red terminal (IGN switch). But perhaps the terminal lost connection from below?

[Barefootdan]

Update! I cleaned and re-crimped the fusible links. No luck. I then made an alligator clip to jump the terminal instead of the fusible link and no luck. Lastly, I ran a jump from the Positive terminal of the battery to the receiving end of the fusible link...viola, power!!
So there is some disconnect from the source side of the fusible link terminal and the battery. I may need to peel back the wiring to see. Unless there is an additional fuse prior to this box?

[Zed Head]

The fusible link block unbolts from the fenderwell easily.  Might make it easier to inspect.

Download the FSM and a wiring diagram and you'll see the full circuit.

 

[Barefootdan]

Thanks Zed Head. I was able to find that jumping the Shunt between the large White and White/Red wire allows for continuous electrical to work. Strange...I tested the shunt separately and saw no issues with the fuse and continuity. I am stumped. I left the jumper in for now to allow me to diagnose other issues. 

Next, I am receiving spark and fuel...but injectors are not firing. I think my coil is not properly sending a signal via pin #1 on the ecu. I ran a jumper to test continuity from the (-) terminal of the coil to terminal 1 of the ecu and I have no continuity. Manually grounding the (-) three times does not fire my injectors as well. Any thoughts on what could cause the disconnect? The manual I saw shows a direct connection. But forums suggest the ignition relay perhaps. For what it is work, I am seeing my tach jump while cranking. Spraying starter fluid in the intake gives me the occasional backfire out the intake too. Plugs are dry.

[Zed Head]

Have yo verified that you have power at the injector plugs?  The EFI system harness gets its power through its own wire which also has a fusible link in it.  Check for voltage at the plugs with the key on.

[Barefootdan]

There is voltage at the plug (at least cylinder #6) when I check at one pin and ground.

[Zed Head]

The Fuel Injection Manual was written for your car.  It shows how to do the electrical testing directly at the ECU connection.  You can test each injector circuit, confirm continuity and resistance and power supply.  

ECU's do fail.  Nissan's final instruction after testing everything is "replace ECU".

 

[Barefootdan]

Awesome, I will walk through that as my next process. So far i dont think it is the ECU since I am not getting a connection from Pin 1 to Coil (-). Fingers crossed!

[Zed Head]

The tachometer is connected to the the coil on the same circuit as Pin 1.  The circuit branches on the way from the coil to the ignition module, the tachometer and the ECU.  I think the split points are by the ignition module.  Find the blue wire at the ignition module and track it back and you might find the branch points.  Nissan used crude crimp junctions to make the branches.  Nasty looking but normal.  Maybe the Pin 1 circuit got pulled loose or the wire got cut.

[Barefootdan]

That could be it...I did take the dash out not too long ago, I may have broken the connection. So my Coil to Tach is good, that is a good hint. I'll do some digging tonight 🙂