Introduction

Inside the Vaitrix box we have:

The gauge itself.

Of note, the pack of fuse taps I bought came with mini-ATC fuses (blue fuse, left) while the 124 Spider uses low-profile mini-ATC fuses (white fuse, left).

For this job it still worked with the supplied mini-ATC fuses, but sourcing low-profile fuses would make for a neater, tidier installation.

As with any job involving electrical circuits, begin by disconnecting the battery's negative terminal.

It takes a 10mm wrench.

Like so.

Remember to engage the yellow locking tab in the up or "locked" position when done.

You now have to route the Vaitrix sensor wire into the cabin where it can plug into the gauge on the dash.

I routed mine back to the firewall and along the back of the steel brake booster vacuum line over to the left side of the engine bay.

To avoid scratching the paint trying to lever the grommet out from under the hood, I placed a loose piece of tape over it from under the hood, then went inside the car and up under the dash above the driver's footwell and simply pressed it out from the inside out.

The tape helps prevent it from shooting out and/or falling in to the abyss of the engine bay.

The plug on the end of the sensor cable is almost the same size as the center-piece of the grommet.

I initially tried just cutting a slot, hoping to slip the plug through, but found the plastic of the grommet too hard for this approach to work, so I ended up cutting a decent size hole in the grommet with a sharp utility knife so I could get the plug through without damaging it.

With sensor wire in place, it's time to move on to the power wiring harness for the gauge.

As mentioned, we're going to tap into the interior fuse block using two fuse taps to get the power we need - 12V+ battery power (i.e. always on) and 12V+ ignition switched power (i.e. powered when the car's electrical power is turned on).

This is the map of the interior fuse block.

I used slots F6 and F10, both of which were empty.

F6 supplies the 12V+ ignition switched power.

F10 supplies 12V+ battery power.

If your car has different options, you may not have the same slots free so you may have to use the fuse taps to power the original circuit as well as the boost gauge, so lets look at how the fuse taps work so you can easily use them either way - in an empty slot or in an occupied slot.

The premise is, you remove an existing fuse, plug that removed fuse and an appropriate fuse for the new circuit into the device, and then plug the device into the slot from which you removed the fuse...and use the pigtail wire on the device to power your new circuit.

But to use it correctly, it has to be plugged in in the right orientation.

The red line indicates that, with no fuses installed, terminal (or leg) A is connected to BOTH of the two slots above it, while terminal B is only connected to the slot immediately above it. 

Now, in your fuse block, if you pull a fuse, one of the slots will have 12V+ (the hot side) and the other will not (the load side).

You have to plug terminal A of the add-a-fuse into the hot side (i.e. the add-a-fuse only works properly one way round), here's why:

Once you install fuses in the add-a-fuse, each pair of sockets is connected (the blue lines). Thus, if we apply 12V+ to terminal A, power flows 1) From terminal A, through the lower (fuse 1) fuse, and to terminal B...this completes the original circuit, independent of the added circuit. Power also flows from terminal A to the left-hand socket of the top (fuse 2) fuse, through fuse 2, and out the pigtail wire. This is the proper way, where both circuits are independent and the fuse sizes do not need to be matched. This is illustrated by the pink arrows.

However, if you plug the add-a-fuse in the other way around (the incorrect way), with terminal B being plugged into the hot side of the terminal in the fuse box, you get the following:

In this situation, 12V+ will flow from terminal B, through fuse 1, and out terminal A, completing the original circuit, and misleading you into thinking everything is OK. BUT...because there is no connection between terminal B and the right socket of fuse 2 (the top fuse), 12V+ will only flow out the pigtail wire THROUGH fuse 1 in series. Again, this is shown by the pink arrows. As such, it is quite possible that the combination of loads on fuse 1 will blow the fuse. Also, if you install the add-a-fuse this wrong way around in an open slot in your fuse box, you have to install BOTH fuses in the add-a-fuse even if you are only powering the one new circuit (this is a big clue you have it the wrong way around)

If you reach in from outside the car to the front end of the cover panel, you will feel a small detent for your fingers.

Just pull the cover off by pulling it towards you.

Here the two fuse taps are installed in the correct orientation in the fuse block.

F6 supplies the 12V+ ignition switched power and will connect to the yellow wire on the Vaitrix power wiring harness.

F10 supplies 12V+ battery power and will connect to the red wire on the Vaitrix power wiring harness.

At this point, you will now have the sensor wire and the power wires in the cabin ready to be routed and plugged into the gauge as shown here.

Routing will of course depend on where you choose to mount the gauge. Keep the wires neat, tucked in, and secured with zip ties so they don't flop about or chafe on anything.

When you are all finished, don't forget to reconnect the battery.

I routed the wires under the dash and then out by the right side of the steering column, mounting the gauge just above the vent, as shown.

The supplied mounting bracket is fairly straightforward and can be stuck in position with the supplied 3M double-sided tape.

The "segmented" nature of the base of the bracket means it conforms well to curves, as was required for this surface.

However, in my opinion, the overall effect is somewhat cheap and cheesy. In no way does it look factory - in fact I feel it very much screams "aftermarket stuck on".

And that's a real shame as it cheapens the whole install in my opinion.

I am very much on the hunt for a better mounting option - one more appropriate for the car and the gauge itself - which is a handsome piece.

Begin by removing the little cardboard protector keeping the battery from making contact in the remote. Just pull it out.

Without touching brake or clutch, press start button once to turn on ACC power.

Aim remote at gauge and press button marked BO – needle will flash.

When you are happy with the setting, as indicated by the needle, press the power button (top left) to exit the programming mode.

Press the start button twice to turn off the car.

Note: If you ever disconnect the battery, this setting will be lost and you will have to repeat the procedure.