Zed Head

So it is a temperature switch. Wonder what it's protecting? Is there a high temperature warning light on the automatic 240Z's? It is odd though that the drawing seems to show it in the cabin on the passenger side. A "thermo switch" used, apparently, only on the automatic cars. p.s. as far as the thread being complete, the question was "what is it" not do I need it. The puzzle is still open! https://www.carpartsmanual.com/datsun/Z-1969-1978/electrical/electric-unit-switch/section-1/240z-260z

The inhibitor switch also has two green wires. Edit - but it's a four wire switch. The seat belt switch has two greens also. Is it magnetic? What would be the actuating mechanism of the switch, if it's a switch. That was one of my thoughts in sugesting a low temperature switch, like AC or heat. You could put in the freezer, and run hot air over it, and see if it closes in either case.

If they have a bad o-ring.

Blowby from combustion can create pressure. But there is also just general leakage and surface coverage from the oil vapor and oil splashed on to the bottom of the cap and cover. Oil tends to spread and cover whatever surface it contacts.

Is there measurable resistance or is it open or closed circuit? Looks like both wires are the same color scheme and have the same connector, meaning no polarity. How about a switch in the AC system? Air temperature.

I was kind of kidding. Didn't know that it was a thing. An odd name for a product, must be from way back. https://www.iqsdirectory.com/articles/wire-rope/aircraft-cable.html https://www.homedepot.com/p/KingChain-1-8-in-x-50-ft-Galvanized-Aircraft-Cable-Kit-with-Clips-and-Thimbles-7x19-Construction-504711/304086908

Can this be found at Home Depot?

Odd. Where did you get the switch? I wonder if it was a bad connection that got fixed while you did the work. The extra stuff. You can use your meter to check continuity through the switch from the power supply wire to the outlets. Doesn't really matter, just curious. I finally understand the inhibitor switch circuitry on these automatics now. Never had a reason to dig in to it before. Thanks for the puzzle.

Since you now know that the head has been off and your hopes for an original engine are gone I would change direction and take time to verify that whoever swapped heads did a good job. Check valve lash and timing chain wear. 1975 has the engine serial number on the ID tag in the engine bay. Compare numbers to see if you got just a head swap or a complete engine swap. The tag is over by the brake master cylinder. Original Nissan parts have a notch on the timing chain sprocket that will indicate wear. Rotate the engine to the zero on the damper pulley timing mark and make sure the driver's side of the chain is tight.

You'll still want to use the paper gasket it with it. I think it might be part of the countershaft bearing shim calculation. Not 100% sure though. And don't lose the shim, it might stick in the cover and you don't realize it's there. The bread trick is to just stuff some bread in to the pilot bearing hole, then pound a rod in on top of it. It generates hydraulic pressure through the bread and will force the bearing out. Don't forget to check the fit of the new bushing on the inpout shaft too. Yum...

Looks like the 4 speed is still in there. You might be ready with a way to stop the engine from tilting backward when you remove it. Some people insert a 4x4 between the valve cover and firewall, others put a jack under the back of the oil pan. Don't forget to replace your pilot bearing. Try the bread trick. Hylomar Blue is popular for things like that front cover gasket. Doesn't harden but seals well. https://hylomar.com/product/universal-blue/

People call it the "M"N47 because it comes from a Maxima. But there's no M in the casting number.

I've probably added a lot of confusion here by looking at things that are indirectly associated with starting. If you want to check if power is making it through the ignition switch I would check for voltage at the black wire with yellow stripe (BY) at the seat belt relay when the key is turned to Start. That is a straight shot, through just one connector, from the switch to the relay. One of the two wires at the plug should have power at Start. The relay just stops it from passing through to the starter solenoid. The thing about the relays clicking is that when you turn the key to Start the Accessory relay opens to cut power to accessories during starting. So the click you hear might not be directly related to your problem. Actually, this diagram frm the FSM clears up a lot, I think. The inhibitor switch controls the starter relay, the starter relay controls power to the solenoid. After checking for power, if you have it, verify that the other BY goes to the solenoid. Then just jump them together as CO suggested. The engine should spin just like jumping it at the solenoid.

I apologize, I am way off my game. Getting lazy. I posted a drawing of the EFI relay. I'll see if I can find one of the ignition relay.

Different relay, borrowed picture from zcar forum but you can see the numbers.

I think that the numbers might be faintly visible on the relay, by each pin.

Here's a place I go to to see what parts might be correct. Found a 75 there, with EGR. Like yours. No AC though so the AC vacuum ports are blocked. https://bringatrailer.com/listing/1975-datsun-280z-43/

Did 1975 California have EGR? Maybe that is a 1975 intake manifold. Just checked 1976 and CA did have EGR. So 75 probably did too. I jumped the gun on the manifold I think. All I'm really certain of at this point is that 1975 never had an N47 head. They did not exist then. I'm going to go with everything is stock except the head and that it's a Maxima N47 head. Which means the head has been off. Maybe other work has been done also. Thanks for the new puzzle.

Pretty sure the ZX cooling fans are turned on by a switch in the thermostat housing. I had a spare ZX engine and messed around with the switch once when I was trying to make my own cooling fan system. I see some other odd things in the pictures. It has the original three piece fuel rail. But it's been messed with, screws are missing. Why not use the ZX or Maxima fuel rail? It's one piece. The AFM number might be important. If the PO used the ZX AFM there might be problems. I'd get all the numbers together and see what's what before getting carried away. I'm not even positive that that's a ZX intake manifold. Maybe it's an L24E unit.

Look by the fusebox and you should recognize the relays.

It could be. That picture I posted in #17 is the one that came from my car. It was bypassed with a wire. Not sure what else did not work before I replaced it. It's not too hard to get to. Unplug it, remove the screws, and pull it out. If you're good with a meter you could do some testing. Post #19. Easy to open also, just bend the tabs back.

The built in tool and parts shelf.

I've thought that only the L24E Maxima N47 came with the cylinder head temperature sensor. Cylinder pressures will be a clue. Especially if it's an F54 block with flat tops.

Oops. Still, check the hoses. My fuel injector hoses were also age cracked and ended up shooting tiny streams of gasoline. Made it all the way to the sidewalk when I opened the hood. Another lucky break, I smelled it in the city before I got on the highway. You have a bunch of small odds and ends in front of you. Have fun.

That would be the cylinder head temperature sensor. That deepens the mystery. It was used in 1980 on the P79 and P90 heads but I don't think the Z car N47 heads got it. That might be a Maxima N47 head. A popular compression ratio "upgrade" for the L28's. @madkaw knows. If you look on the driver's side by the engine mount you might be able to see the block casting number. It should be N42 or F54. I was going to mention the fuel hoses. Make sure that they are all high pressure EFI hose. I'm pretty sure that that glass filter is not rated for 36 psi. Check the rubber hose in the back from the fuel pump also. My car had low pressure hose when I got it and it split while I was driving. Luckily a UPS drive saw the fuel spilling and flagged me down.