An air fuel gauge is a popular add-on for the Subaru WRX. This gauge receives a measure of the air fuel ratio that is being supplied to the engine. The gauge takes the reading from the oxygen sensor, which is already installed in the vehicle. The gauge will allow you to check whether your engine is running rich or running lean. Running rich means the balance of oil and air is oil-heavy. Running lean means that the mixture has too much air. This can be adjusted to improve the engine's performance and to reduce the pollutants produced by the vehicle.
Disconnect the negative terminal of your battery by unscrewing the negative terminal from the negative post.
Use the template provided in your kit to pre-drill mounting holes for the mounting bracket in the location you choose for the gauge.
Attach your mounting bracket to the dash location with the provided screws
Route the red wire from the back of your gauge through the grommet in the driver's side foot well. The grommet is a rubber plug that closes the engine compartment off from the interior of the car. The hole is there to allow you to run wires through the firewall of the car and into the inside from the outside, or vice versa.
Connect the red wire to the positive terminal of your battery. Connecting the wire is as easy as disconnecting the positive terminal from the positive post, and adding the red wire into the harness that plugs into the terminal.
Connect the black wire from the back of your gauge to any grounding metal surface on your vehicle.
Route the orange wire from the back of your gauge through the grommet in the driver's side foot well.
Route the orange wire to the front center of the engine where the bulkhead engine connectors are located. The bulkhead connectors are located near the driver's headlight. You'll see several wires running into a black plastic box. The plastic box contains the ECU, which is the engine control unit, or the computer that allows the car to run.
Splice your orange wire with the B17 wire connected to the O2 sensor. Use the wiring reference for clarification on the exact location of the connector and the location of the wire on the connector. Cut the B17 wire that is going to the O2 sensor. Strip 1/4 inch of wire on both ends of the wire that you cut. Strip 1/4 inch of the end of the orange wire. Twist all three of the stripped ends together. Solder the twisted wires together. Wrap your heat shrink around the wire. Plug in your heat gun and warm the wrap until it shrinks down onto the soldered connection.
Splice your orange wire with with the wire that connects to B17 pin on your left-side connection. To splice the wire, strip the end of the insulation off to expose approximately 1/4 inch of copper wire.
