Hey guys, this thread was super helpful so thanks for all who have contributed. I discovered a couple of thigs along the way that I thought might be worth sharing, particularly re-using the wiring that's already in place for the original OEM boost sensor to give power (sensor is seperate, although there is a small grommet behind the clutch master which makes running that a sinch)...
Hope this helps.
S15 Boost Gauge Wiring
Stolen information from several places on the internet and added a little of my own including pics with the intention of re-using the original wiring that is in place to get my Defi gauge up and running.
Mostly here:
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Pin out
From the car
Pin 1
Red/
Blue: Illumination power supply. Key-on, 12v with light s/w on.
Pin 2 Black: Illumination ground. Key-off, 0v.
Pin 3
Green/
Yellow: Ignition power supply. 10A fuse. Key-on, 12v.
Pin 4
Red/
Black: Constant power supply. 10A fuse. Key-off, 12v.
Pin 5 White/Green: Boost sensor signal. Voltage varies with signal (1.2 – 2.5v approx.)
Pin 6
Black: Gauge ground. Key-on, 0v.
Fig 1
Pin out
From the boost gauge
Pin 1 White: Illumination power supply. Key-on, 12v with light s/w on.
Pin 2 White: Illumination ground. Key-off, 0v.
Pin 3 Red: IGN - Ignition power supply. 10A fuse. Key-on, 12v.
Pin 4 Red: Constant power supply. 10A fuse. Key-off, 12v.
Pin 5 Yellow: Boost sensor signal.
Pin 6 Black: Gauge ground. Key-on, 0v.h
Fig 2
Soldered and connected
Twist the unused wires together, then strip the wires you will need paying careful attention to the two red wires coming from your plug. One of these will match the Defi colour scheme and the other will match the orange out. I used a sharpie pen to put a black line to make the distinction.
Fig 3
The plugs in the photos are oriented such that they would plug in together, and the pins start by counting the side further away from you with two wires first from left to right as shown (1 and 2) and then the closer side with four wires (3, 4, 5 and 6) - I've bolded the wires that match up with the Defi Racer guage as that's what I was fitting. To do the above you will need to cut the wires from your OEM gauge, so if you want to keep it and possibly re-use it then make sure to leave enough wire... For me, mine was too temperental anyway so if I sell the car the next guy gets it. The car deserves a decent boost guage so I'm cool with this and I don't plan on letting it go any time soon