Sure, here it is:
https://imgur.com/6QKmbk6

this is what is important:
https://imgur.com/VPwYc0i

The cable has 4 wires, Black, Red (+ and -), Orange, White.
The white wire can be ignored, as it's used to provide white illumination.
On the right side you can see the combinations for different lightings, and the one with orange wire is what I'm after. I'm only confused with where I'm supposed to connect it.

OK, in terms of the orange wire, I'd suggest reviewing the posts under this heading:

Defi Oil Pressure Gauge - Need Advice

If you have a copy of the FSM for your model year, you should be able to locate one or more connectors with a wire marked ILL(+) that form part of the main harness. If you splice into one of these wires, the gauge should illuminate and also dim when the headlights are turned on.

Hey, thanks for the help, but I still have a problem identifying this completely.

So...I have the FSM. I do get it - that I can put the (-) to any of the chassis parts, and that the (+) or the Orange wire can be connected to the ILL(+). So If I connect the (+) wire there, where do I put the Orange one? Or better yet - If I connect the Orange wire to it - then what do I connect the (+) to? Probably not the battery....or?

Connect the (-)wire to a ground location on the chassis.

Connect the (+) to an add-a-circuit that you can install into one of the circuits found in the fuse box located on the left-side of the driver's foot well. The individual circuits are identified on the inside of the fuse box cover. Pick one that is powered when the ignition is on.

Connect the orange wire to one of the wires shown as ILL(+) in the FSM. I chose the ILL(+) wire that illuminates the radio controls. If you want to do the same, follow the instructions in the FSM for accessing the rear of the radio. One of the connectors at the rear of the radio will contain the ILL(+) wire that you will need to tap into.

Trust this helps.

Gonna follow up with my DIY here, as I figure if someone will want to install the pressure gauge in the ventilation duct, might as well help them a bit. I don't have full picture thread but I believe text instructions will help enough, with some pics for reference.
I chose this position for the pressure gauge as it's the most non-intrusive, original looking way of having an oil pressure gauge in the Z, and it looks really awesome.

I got the inspiration from the forum member Setluky http://www.the370z.com/diy-section-d...ure-gauge.html
I began with getting another ventilation duct, just so that I can keep the original in case I screw anything up. I cut out the ventilation grilles and places the pressure gauge inside. No documentation about these steps as I think most pressure gauges might differ with size so do this part and measuring on your own, it's not that hard. That's the easy part.

I completed the hardest part today, finally. So let's cover the basics:
You remove plastics on the door sill, in the foot well (both are just snapped on, footwell has one easy screw).
The door panel is removed via 3 screws, everything else is snapped on. Once you remove the door panel, there will be wires holding the panel still.
Unlatch the connectors (they have one tooth in the middle that needs to be pressed so that you can unhook them). After that you're ready to begin the fun part.
Remove the speaker. There are 4 bolts around the speaker, and 4 bolts directly on the speaker. Remove these "inner" bolts. The speaker is then still hooked with some plastic notches and then you've got one connector on it. Now you're coming to the difficult part.

This is what you'll be looking at:
https://i.imgur.com/rQs5HOph.jpg

Now you want to pull out the rubber covering the wiring loom between the door and the chassis:
https://i.imgur.com/TvMgKa4h.jpg

It is very snug on the door side and when you pull it out, you'll notice a tab is glued to the wiring loom. This part needs to be cut, it will not affect anything else other than give you access to push the wires through it, to the cabin.

In the footwell, locate that connector that's connecting that wiring loom from the door to the cabin. NOTE: you cannot just pull it out, don't try it. The way to disconnect it is very very interesting. The dude in this video explains it nicely: https://www.youtube.com/watch?v=tRa7BnONILo look at the video at 5min mark. Use a very thin long screwdriver to start moving the tab that keeps the connector in, but then proceed to nearly close the door fully so that you can pull the tab all the way down until it will disconnect the connector. Then open the door back and you'll finally remove the connector from the chassis.

The connector on the outside, already has a hole in it, so that wires can easily go through the door, through the rubber hose, through the connector - but they can't enter the cabin. The connector on the cabin side, entering the footwell, has no opening. This needs to be cut.

Now that you removed the connector on the outside, in the footwell, you can now remove the connector - it has just one notch on the bottom side holding it, on the outside between the door and chassis.

This is what it looks like after I cut the opening for the wires:
https://i.imgur.com/D6fnCerh.jpg

If you don't cut this empty part of the connector, you won't be able to guide the wires through the connector. I just used a sharp knife to make a small cutout. Pushing the wires through is a challenge.

I also disassembled the connector on the outside of the car because you need to remove the rubber from it to be able to pull in the wires through it. Just examine it thoroughly and you'll realize what needs to go where to disassemble it.

I then used a long thin knitting needle to push it through the rubber wiring loom, between the outer rubber and next to the wires that are guided through it. I then used sticky tape to tape my wires to it and then pull them through it. This is fiddly, annoying, very tight, all done in a stupid position between kneeling and sitting on the door sill and I advise you to have patience with this.

You should end up with something like this:
https://i.imgur.com/vagf7RNh.jpg
https://i.imgur.com/6KhKJJqh.jpg

Note that I pulled the wires out of the door through one of the upper coverings, as the bottom will be covered by the speaker and can't be used.

You now need to push these wires into the cabin and then reconnect the connectors. I first tried to just hook back the footwell connector back to its place, and then push the wires but that proved too hard, so I simply guided the wires to the cabin, through the connector and then connected it all, while making sure I keep the wires tight enough so that they don't get pinched in the process.

If you have similar color wires, make sure to label them so you know which is which.

Hardest part done, looks just like original, nobody could tell anything went on here:
https://i.imgur.com/TnY0vpch.jpg

And then very simple reassemble of the door panel, but with the pressure gauge position instead of the ventilation duct:

https://i.imgur.com/iYD8b6sh.jpg
https://i.imgur.com/8wevXCxh.jpg

Why isn't it turned on? Because now comes the part to actually connect these wires somewhere! I don't know where lol. I'll post another post now with my questions :)

So, with wires to the pressure gauge finally in the car, I need to hook them up somewhere.

Wires 1:
These go to the pressure sensor. The pressure sensor will be mounted to a T-fitting to the engine block. How do I go to the engine block from the driver's side footwell? I guess there's an opening somewhere in the firewall? Any tips?

Wires 2:
The dreaded wires that need to power up my pressure gauge. I still have no idea where to hook them up. 40to332 member already gave some great tips up in this thread, but I'm still a bit lost. I checked the fuse scheme and this is what I have:

https://i.imgur.com/qkQumQ1h.jpg

Where should I tap into? Also, how do I do it exactly? It seems way too tight and too little room to cram another wire in there, to add it somehow in the loop. Any ideas on how I would to that?

Thanks!

OK, after rereading what the kind member 40to332 told me, I only just noticed it's my english knowledge (or lack thereof) that held me back here.

Add-a-circuit I had no idea what it was, and now I found out, and yes, that will definitely solve the problem of tapping into the fuse :) I ordered two now (one for backup in case I want to add whatever else), so I guess that will solve it.

In the meantime, I took some time today to continue preparation for installation, I pulled the sensor wires through to the engine bay. What I found easiest is to guide the wires from the driver's footwell, in front of the shifter, then to the passenger footwell, and then via the cabin filter slot. There is a soft foam "wall" above the cabin filter and I guided the wires through that. They go out in the engine bay right below the plastic cowl that is located under the windshield. It's not the best solution, but it'll work. I fixed the wires so there's no rubbing on the chassis and left them near the battery for now.

Alright, so I finally received the add-a-circuit wire (took 2 weeks to arrive), and I finally powered up the pressure gauge!

One clarification would be GREATLY APPRECIATED, if someone would confirm. I grounded the black wire, and I'm left with red (+), as well as orange (amber color of the gauge). I tried to connect either to the blower fuse (seems like an OK fuse to add this), but the pressure gauge wouldn't work. However, When I plugged in BOTH of these wires together, red(+) and orange (for amber color), I got it working immediately. This orange was suggested here to be added to the radio or dimmer or similar. I like this way as it is - I'm only wondering - is it OK to have them connected together like I did? Or should they be separate?
Thanks anyone who spends yet some more time to clarify this to me (an idiot here). :)

OK, a couple of things:

1. If I recall correctly, I tapped into the CIGAR LIGHTER circuit. It's a switched circuit. I never use the lighter so I wasn't concerned about powering the gauge through this circuit and blowing the fuse. If you use the BLOWER circuit, you may want to pre-check that the fuse will not blow when the gauge is connected with the blower fan running full on. I expect the fan draws a fair amount of power. In other words, with the gauge wires connected, turn the blower fan on full and make sure the fuse can handle the additional load. You may be OK since I suspect the gauge doesn't draw a lot of power.

2. Based on your description, both the red (+) wire and orange (illumination) wire need to be connected to a power source for the gauge to work and light up. If you're OK with the gauge light being on full when driving both during the day and at night, then connect the wires as you've described. In my case, I wanted the gauge light to dim at night so I went with a different wiring scheme that resulted in the gauge light dimming when the headlights were turned on. This required tapping into one of the wires that illuminate the radio unit. It's a more complicated and time-consuming wiring scheme than the one you've described.

Trust the above helps!

Dude, thanks a whole lot for your help and inputs. I really really appreciate it. Here's a virtual beer
https://i.imgur.com/ms8UVFrs.png

I'll see what it will be like, but I believe it will be just fine if the gauge is fully on, as the amber lighting isn't too bright, and will suit the inside of the car just fine. If it turns our it's way too light, I'll then hack it to the radio switch or something.

Also, thanks a lot for the tip about blowing the fan to check if the fuse holds up. That fuse is 15amps, so I'll see if that's OK, otherwise I'll go check other options.

Thanks once again!

I'm having troubles with my oil pressure gauge, and I have no idea why.

So what happens is - my fuses (10A) are blowing non-stop.

Let me run you through the current setup and situation:
-The pressure gauge is added to the fuse box via add-a-fuse on the blower/audio slot, and I used 2x 10A fuses to run it.
-It was running well for over a year, but last year it started to show weird readings - as if everything was shifted up by cca 30psi. For example: instead of showing 20psi in idle, it would show 45psi. On full gas it also showed too high reading. It did once go back to normal, but usually showed too high.
-So over the winter, I bought a new oil pressure sensor, figuring that my old one might be broken and replaced it.
-First moment I connected it, it blown a fuse. I switched wires on the sensor, figuring I might've misconnected them....it then worked - but again broke very soon.
And ever since - it's been blowing the fuse basically within a minute or few whenever I try to run it.

I tried to change the wiring for the pressure gauge - but it didn't work. Below I'm quoting the pressure gauge diagram... and just for info - I had it connected with both orange and red wire together - and to the fuse. I figure that's OK....but blowing the fuse confuses me.

Any ideas? Thanks in advance.

OK, so as I understand things, you installed a single "add-a-fuse" to the blower slot in the fuse panel. The add-a-fuse should have two slots ... one for the original factory fuse and the other for the fuse for the new circuit that powers the pressure gauge. It appears from your post that you installed a 10 amp fuse into each of the two slots. That may be your problem. The blower circuit requires a 15 amp fuse. I'd suggest referring to the instructions that came with the add-a-fuse and identify the slot that corresponds to the blower circuit and replace the 10 amp fuse with a 15 amp fuse. You can keep the 10 amp fuse in the slot that powers the new circuit (i.e., the pressure gauge) since the gauge itself will draw little power (i.e., less than 10 amps). Alternatively, read and follow the instructions below:

It appears that you're running both the red (+) wire that powers the gauge itself and the orange (illumination) wire that controls the lighting in the gauge from a single add-a-fuse. I'd suggest installing a second add-a-fuse. You can install it in the cigar lighter slot in the fuse panel. Use the original add-a-fuse to power the illumination circuit (i.e., connect the orange wire to it). Use the second add-a-fuse to power the gauge itself ( i.e., connect the red wire to it). Fuse selection should be as follows:

Original add-a-fuse : 15 amp fuse for the blower/5 amp fuse for illumination (orange wire) circuit. (According to the instructions in your earlier posts, it's rated at 2 amps).

Second add-a-fuse: 15 amp fuse for the cigar lighter/ 10 amp fuse for the gauge (red wire) circuit).

Trust the above helps!

That is correct! The add-a-fuse has two slots, and indeed, the on that's blowing is the oil pressure gauge fuse. From what I read online, I figured that 10amp should be more than enough, so I didn't go with a stronger one.

I have another add-a-fuse so I'll try to run the other wire separately, as you suggested.

Thanks A LOT for your detailed help! I'll post results once I manage to do this.

Just connected another add-a-fuse and it works! The pressure gauge fired up, no problem, all good!
The only question now is whether it actually shows correct pressure. I didn't drive it yet, but even when I just put the ignition to Acc, it's showing 43psi, which I find weird....shouldn't it be on 0 until I turn it on?

Should be zero until the engine starts.

I agree. Perhaps you f'd the sensor during the course of blowing multiple fuses. You might try installing another new sensor ... now that the wiring problem appears to be solved.

That issue appeared with the old pressure sensor! That's why I replaced it in the first place. And the new one shows exact same behaviour. This is why I'm suspecting something might be wrong with the gauge itself...

I'm not ruling out that the gauge itself may be at fault. However, my understanding is that when the problem first appeared with the old sensor, the fuse(s) were being blown. Then you installed the new sensor and the fuse(s) continued to blow. The new wiring scheme appears to have solved the problem with the fuses blowing. But both sensors suffered the blown fuses and both may have been f'd. So it could be that the sensors were damaged, leading to a wrong signal being sent to the gauge. Or, it may be that the gauge was damaged when the old wiring scheme was in place. I guess the choice becomes whether to replace the gauge and see if that solves the problem or install another new sensor and see if that works. I suspect the sensor would be the cheaper option.

You are completely correct in everything you said, and thanks for that!

I gotta say though - if I decide to again replace the sensor, I must go through the hassle of changing the oil again (or recirculating it), and that still might lead me to nowhere. Alternatively - if I go with the expensive option of checking the gauge - I can quickly check it, and if that isn't the solution - I can still return the gauge and get my money back. So I'm actually leaning towards that option....

Ok, I just had another idea. I can always unplug the sensor from the pressure gauge and see if it dials to zero when turning on. If it doesn't, it's obviously the gauge problem.

Agreed ... that's worth checking.