I have just recently installed Apexi's RSM-GP, Rev/Speed Meter with G-Sensor. It was purchased from:
The install took me about 1 hour but should take no more than 3 hours depending on your mechanical skills. Apexi includes all the wiring harness' and connectors you will need. What is doesn't provide however is an English Manual and Wiring Diagram. However you can always DL one from thier site via PDF files, you'll need to have Adobe Acrobat installed to view the files:
The install was pretty simple for the WRX. Since there is no rev/speed limiter on our cars, only 4 wires had to be spliced into the ECU. Ignition power, Ground, Speed sensor and Rev meter. Apexi doesn't list any cars newer than 2001 in thier diagrams. I was able to get the ECU wiring diagram from:
The diagram is pretty wierd to look at since they view from the pin side not the wire side. Take some time to look it over before installation so you don't get confused. Also the Middle section "E" is actually the middle plug on the ECU and "C" is the plug second from the left.
Other than that the only other time consuming part is getting the Foam stand for the G-Sensor perfectly level. I used a sharp x-acto knife to cut the foam. I also used a level to assure the G-Sensor was flush so it could take acurate measurements. There were 3 wires attached to the sensor. The manual or wiring diagram doesn't explain what they are so I opted to just tape them up and tucked them along with the remaining wires. I sure wish I had a digital camera so I could post some pics of it. It looks and works pretty nice. Until then...
BTW the G's calculated with the CUSCO Swaybars are off the hook!!