Captain Obvious

Wow that looks fantastic!! Was the installation process nerve wracking, or did it all go smooth?

I suspect the explanation is nothing too nefarious... I'm thinking the photographer just screwed up and forgot to take a straight on left side pic and then tried to hide his mistake by mirroring the right side and photoshopping the decal. They shouldn't have done that, but I'm guessing it was something like that. It's not like the left side of the car is all caved in or anything. There are other shots from the left that show it's OK. Except for that exhaust. LOL.

Oh, and while you have the gauge on the bench... The two voltmeter connections (Black and black with red tape) should be completely isolated from everything else about the gauge, including the metal housing. Take a resistance reading between those two wires and gauge housing metal and it should show no connection. And the other ground (the one for the fuel gauge) should be the opposite and should be tied hard to the gauge metal housing. Check that one too. I'm just still a little bugged by your waving voltmeter test that started this thread. I still think the problem was either simply just the wrong wires used or a source impedance issue with your motorcycle battery getting pulled down by the additional load of the fuel gauge, but I'm just looking into other possibilities while you're in there.

OK, I found a spare volt/fuel gauge here and it's the same as the one in your pic, so I think we have a solid point of reference. I added descriptions to the wires in your pic trying to show the functions. Important to note that the wire colors here ARE THE WIRE COLORS RIGHT AT THE BACK OF THE GAUGE. The reason that's important to note is that Datsun SOMETIMES CHANGED THE WIRE COLORS AT THE DASH CONNECTORS, and I believe the volt/fuel gauge is one of those situations. So be careful when referencing wire colors on the wiring diagrams since they sometimes changed colors on the gauge side of the connectors. In other words, the colors on the diagrams are the colors that exist ON THE HARNESS SIDE, and not always on the gauge side. But all that said... Here's what the wires do right at the back of the gauge: Most of the connections are unique and should be relatively easy to identify on the dash side (assuming things aren't TOO hacked up), but there are two connections that are not. There are a) two ground connections, and there are b) two "hot in ON and START" connections. a) The two ground connections just go to ground and there's no real requirement for them to be kept separate. If you wanted to for some reason, you could just connect those two to the exact same ground location. b) The two "hot in ON and START" connections originally went to two different fuses in the block, but if you get really stuck and just can't deal with it anymore, then it probably doesn't matter much which fuse get's which function. But if you really want to figure out the real-real correct fuses, we can work through that too. So with the different years and different PO's in there, I think it's going to have to be up to you to find the correct connections on the dash side, but that's what they should be connected to. Is that enough excruciating detail? Hope that helps!

Cool. I think I have a loose volt/fuel gauge around here to snap some pics. Just to make sure what you have there is the same as what I have here. I think that with the mix-match of years/harnesses/parts, etc, we need a solid point of reference. I'll see what I can find.

Well I'm not really sure what would be the best way to proceed here... I've got two proposed ways to go forward: 1) We can go over the exact three wires would be needed (in excruciating detail) to confirm or deny your waving voltmeter phenomenon on the bench. 2) We could skip the above step and I could document (again in excruciating detail) what each of the wires on the back of the gauge SHOULD connect to and leave it to you to find the corresponding wires on your car (because your dash harness is non-stock and I don't have reliable documentation for what's where. Those are my thoughts. What do you think would be best?

My non-expert thoughts on the matter? Most of the fuel injection systems have a long-ish intake tract and some sort of air flow meter along the way towards the air cleaner. Both of those restrict the air flow. Might not be much restriction, but it's more restriction than a short stub of a carb throat running wide open. For example... When they went to the fuel injection in the 280Z, each cylinder got a whole lot less throttle plate cross sectional area to the air cleaner than they did when they were running carbs. In addition, the fuel injection system has that AFM flapper thingie which adds some restriction. So while it's absolutely POSSIBLE to design and install a FI system that provides no additional intake restriction over a typical set of carbs, I think it's cheaper for the manufacturer to use something that shares components like throttle body and air flow meters. I don't think the manufacturers went to fuel injection because of performance. I think it was because of driveability, fuel economy, and emissions. So I'm no expert in the field, but my take is that for most stock automobiles these days, if you're willing to forgo wide temperature range drivability, fuel economy, and emissions... I think you can get better straight up raw performance from a carb or a bunch of carbs. Maybe a set of ITB's and a huge MAF that doesn't provide only negligible restriction could be the same as carbs?

Haha!! I think you've been lying in wait just looking for the opportunity to use that!

And about your dash gauge color... I changed my Z over to white and never looked back. I had amber in my late eighties Pontiac Fiero and it was cool. For about a week.

So it sounds like this is a non-stock application where you're putting a 280 gauge into a 260? Do you know what year is the gauge? And by the way, forget that stuff I said earlier about the grounds for the voltmeter and the fuel gauge being tied together inside the gauge... They're not. I was not reading the FSM diagrams correctly. The two black wires at the top of the gauge (one solid black and the other is black but has a red wrap of tape on it). Those two are for the voltmeter. I assume the one with the red tape on it is positive and the other is negative. Those two come out of the back of the gauge at 12:00 ish when looking at the back. And then the voltmeter ground is the other black wire that comes out of the back of the gauge at 8:00-ish Those are the three wires you're working with?

Forget all that stuff I wrote here. It's wrong. Oh, and by the way... The ground side of the voltmeter and the ground side for the fuel gauge are already connected inside the gauge assembly. So when you say "you're connecting the fuel gauge ground"... I'm not really sure what you mean by that. In other words, there is no fuel gauge ground accessible outside of the assembly. There is the fuel lever sending unit connection, but no ground. So if I had to shoot from the hip here, I would guess you're connecting the wrong wires somehow.

That wiggle is caused by the temperature/voltage compensation circuit built into the fuel gauge portion of the meter. But that said... the wiggle should not be happening, so let's explore a little. It looks like a source impedance issue where the amount of current you're pulling from your source is dragging the supply voltage down. The question is "But why?" How many wires are you connecting on the gauge? Two for the voltmeter, and a third when you bring the fuel gauge into the picture?

@Mike

@Mike

Maybe they were designed like that. Variable rate progressives. The lower coils bind on big bumps. You know... Like when you let it down off the jack.

Hahaha!!!

Welcome back Zedy. You're our only hope.

If the booster is in good shape, it should hold vacuum. You'll need to put a check valve (or manual shut-off valve) on the vacuum source side so you don't lose vacuum back-flowing through the vacuum pump when you turn it off, but other than that, the can should be sealed.

Oh, and your steering wheel coin... That's about the size of a quarter, right? That's going to take a long time to mill out all that detailed recessed area. And I'm sure the reason you're going to powder coat it is to hide the tooling marks, right?

Cool. I've not looked for makerspaces in my area, but that is something I should investigate. Been meaning to, but keep forgetting. I did pick up an el-cheapo CNC router not long ago and have made a few parts similar in concept to what you're trying to do. "They say" it's capable of doing some light duty milling in aluminum, but I don't think it's rigid enough. Everything I've cut so far has been plastic. So far, I've followed my typical pattern... Spend about half the time improving the machine and fixing the flaws with it, and the other half the time actually using the machine to make parts.

Haha!! Exactly who I was thinking of when I wrote that! Thanks for picking that up! Ack!!

Hahaha!!! It's true!! In fact, I just got a new one! And... I hated it so bad* that after a short usage time (one month maybe), I just got ANOTHER new flip phone of a different brand. The new-new one is more advanced than my previous flips. I handed it to my son yesterday and in a matter of minutes he was laughing at funny videos on youtube. So it's got that. I might never use it for that, but it's clearly capable. So ppppbbbbhttttt for all you guys who think I'm stuck in the 1990's. Hahaha!! * IMHO, it should have never left the factory. If I wrote the software on that POS, I would have been fired on the spot.

Stealing a stock Z? For me... Gone in 60 seconds and I wouldn't care at all whether the security screws were broken off or not. You need something more elaborate than that. Great list. Let me add... Break a window, reach in and open the hood, disconnect the steering coupler donut, jumper the starter solenoid, and then use the starter to crank the car to your place while steering by kicking the front tires in the direction you want to go. Bring extra batteries just in case the PO was having alternator troubles. Or a charger and a really long extension cord.

Yeah, I'm not sure I did a good job of putting my thoughts into words. Av8ferg did a much better job than I did. So let me try again... So you think this forum exists for the purpose so you can ask us every question and you don't have to do any research yourself? is that why we're here?

Yes, they're all polyurethane. The question is "what are the characteristics of the polyurethane?" Just because they're poly, doesn't mean they're "the same". It's like saying "they're made of plastic". But I'm sure you already knew all that.