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The pits!

Ok, got it back together Check for continuity between the alternator output post wire and positive battery cable, which it did. Started it up, and got 14.8V at the battery........ so that's a good sign..... I did leave off the positive wires for the circuits that were hooked up to the positive battery cable: Headlight Relay Upgrade Parking Lights Relay Upgrade Driving Lights Stereo I will work and check those circuits this week. I suspect now that either the alternator was/is flaky, or one of the wires coming off the alternator might be flaky. I will start it up with and wiggle the wires with a meter connected. Not sure if I am happy or confused....... Any other advice on what to check?

Probably need to put some thought into replacing the short lines. You need to do an evaluation of what condition of the parts you’re working with.

MAN remember the heady days of me celebrating that it was just a matter of screwing something in? Man those were the days. I took it out tonight and within about a minute or so of using the brake pedal it went pretty much straight to the floor now that it was stopping mass I guess. I headed back home and now there is fluid leaking out of the bottom of both where the front and rear brake lines screw in. Time to trash this master, right?

It got a nice price when it had the L6. $46,200. Not sure that 454 is going to add value. I'd guess most of the aftermarket parts went on after that sale. No driving video yet. 1971 Datsun 240Z VIN HLS3042112 | Hagerty Valuation ToolsHave you seen this 1971 Datsun 240Z VIN HLS3042112 auction result?

Grab a torch - propane will do - and melt the body lead out of that section. That'll give you a better idea of how that sheet metal is shaped and spot welded together. There will be body lead in various places all up and down that pillar. The lead will probably have saved the sheet metal up near the window flange - and may give you a good clean section to weld to at that end.

I was describing its function, not the actual material wire. The trigger wire for the new tach is its own independent circuit. I was also trying to tease out if you're replacing the stock tach or adding another tach. Are you sticking the new tach in the hole where the old one is? Your other basic question might be "how do I keep my ignition system functioning if I remove my factory tach?". Since they are tied together in the 240Z's. Just breaking the "how do I connect my new tach?" question in to its elements. Seems like you're on top of it. Good luck.

But if you look at the diagram, the G/W gets Battery Voltage in the START position of the IGN Switch. (The circuit provides a bypass of the Ballast Resistor when cranking the engine for start - once started the juice goes through the Ballast Resistor for normal running operation) SO - don't leave the G/W dangling where it could cause a short... could have done that in one post - but I'm old...

Very good idea with one caveat - the stock wiring is "50 how many" years old and could be pretty oxidized (engine bay). My OCD would be "new gauge... OLD wire? Naw...". Your mileage may vary.

Good advice, just got home from work, will go put the alternator in. I assume I should see continuity from the alternator output wire to the positive battery cable? Will check that before I hook up the battery and see if there is 12 volts on the "T" connector with the key on.

Well, I certainly could run a new, and completely separate wire from the coil "-" through the engine bay, through the firewall, and to the existing yellow wire to run the Speed Hut tach. But, the existing B/W and G/W wires basically already routed in the stock wiring harness from, and to where I need to go, are made completely redundant by doing so. Why not repurpose one of them and save the time and effort to run another wire? Looking at @SteveJ's wiring diagram that shows after modifications, I see that he chose the B/W that originally went from the coil "+" to the stock tach 4 prong connector as the wire to repurpose for use with the Speed Hut gauge. Of the two original wires (B/W and G/W), only the G/W wire has no purpose after this modification. I've got some other wiring that I need to figure out how to route as well. For example, I need to wire in a coolant temperature sensor and harness for dual electric fans, and the wiring for oil pressure, oil temperature and coolant temperature senders. So, I will be thinking about how best to route those through the engine compartment and where necessary, to the gauges in the dashboard. I am set for information I needed to wire up the tach - thanks to all who responded!

Fixed it for ya! 😁

Don't know what it is but it isn't a Z

That's the first Z conversion I've seen that I like. That said, I'd like it even more if I didn't know it is (or was) a Z.

I have been using that bosch relay in the photo since 2012 and no issues. Plugged in a go. The bosch relay was used in the first 280Z in 1974. Datsun used a Bosch L-Jetronic system for the first 6 months of the 280Z production And Hitachi copied it. That is why a lot of Bosch parts will work on these efi systems. I think @Mike had a bosch system in his attic once. I posted an ebay link back in 2018 and it still works😄 https://www.ebay.com/p/77006951

Well... it started life at Pierre's Z... saw it in 2001 at the Motorsports Auto Show. The best looking Z Convt. conversion I had seen. The body lines were beautiful..

What changes did he make to get all the plugs firing evenly?

Everything you need is here on CZCC.com The relay you show is not just the fuel pump relay it's a combined fuel pump and EFI relay. The relay that EuroDat showed is the proper replacement. It was used from 1975 through 1977. In 1978 Nissan separated the two relays. Nissan calls the EFI relay the main relay. They don't usually rust like yours because of their location. I'm still impressed by the challenge that you're taking on. Remember to check for shorts to ground before connecting the battery after you fix things. Those original pictures look like a wire fire waiting to happen.

It's a voltage triggered tachometer. Like those in the 280Z's. The yellow wire can, and should be, completely separate from any of your existing wiring. To run the Speedhut tach. Seems like your real question might be "what do I do with the wires from the old tachometer" to keep things working correctly. If you're replacing the stock tach. If you're keeping the stock tach, you could just leave it untouched, and wire in the new tach using the instructions. It won't affect the ignition system, since it just senses the voltage changes at the coil negative terminal. Just offering a reinterpretation of the original question. https://speedhut.com/content/instructions/2_and_2_58_tach.pdf

Here's an interesting one. A Pierre’s Z Service Center creation, apparently. https://bringatrailer.com/listing/1971-datsun-240z-345/?

Are you talking about the white and white/red wires at the fuse box? They branch off the wires going to the ammeter. I suggest not speculating too much. You will confuse yourself. Don't throw parts at problems. Diagnose.

ok, that was my next question, is the ampmeter bad? But the car does run and start, so I can eliminate that? What about the two big wires that have connectors by the fuse box?

FYI, I diagnosed a bad EFI relay on a 77 and told the owner to get the relay that @EuroDat said to buy. He got that relay, slapped it in, and the car ran just fine.

To combine what we talked about on the phone with the guidance from @cgsheen1, here is the stock wiring. This is essentially what the modified wiring would be.

While the wiring diagram shows a fusible link at the alternator, I personally have never seen it in the wild. The output from the alternator goes to the battery through the ammeter. If you do not have continuity from the alternator output to the battery, that usually indicates the ammeter failed or the fusible link at the starter failed. In either case, the car would not start/run (unless it was hacked up by a previous owner).