For the A/F guage, you don't need to tape the ECU wiring harness. And actually you probably should do it that way. Instead, run the wiring to the engine bay and tap the O2 sensor line. For the 9000 Im not sure what color you tap, so maybe others know.
I've installed an A/F gauge in my 94 Aero. There is a connector just aft of the engine, down low, and very close to the oil filler tube. It's held in a rectangular bracket. To disconnect, I had pry the red side tab outward. It's a locking type connection. I made the splice (using solder and an environmentally sealed heat shrink tube) on the ECU side, not the sensor side of the connection. If you place it on the sensor side, you'll have to resplice the gauge in when you need to replace your O2 sensor.
Keep in mind that this is for a 94 Aero with a heated O2 sensor. I don't know what diffs may exist between our cars.
I had to cut the insulation back a bit on the ECU side to see the wiring colors as the O2 sensor will have two whites coming out of it. I also needed some room to make my splice. In my car, Blue/Red is Heater Power (12VDC), Black is O2 sensor Low, and Grey is O2 sensor Hi. Pins 1,2, and 4 respectively at the O2 connection aft of the engine.
Correction to my first post... Black would be Sensor Low on a 4 wire sensor. We have 3 wire sensors. Black is chassis ground for the heater element internal to the sensor.
Now to answer your question...
I removed the top of the dash. I connected the signal wire for the A/F gauge to the grey wire. I ran a 22 AWG wire from the grey wire following a wire harness up to where the A/C hoses run into the passanger's side of the cabin. There I used a wire hanger from the engine bay and fed it into the cabin. Once the hanger was fed, I taped my 22 AWG wire to the hanger end in the engine bay and pulled the it all through. I ran the wire along under the top of the dash to the driver's side A-pillar. I used a local chassis ground and the ingnition switched 12VDC at the headlamp control for gauge power. The switched 12VDC was on any of the three ALL YELLOW wires going into the back of the light switch. I spliced into one of the small ones (3 total). Check the wires for power using a multimeter. It should read 12 - 14 VDC when the ignition is switched to the ON position and 0 when switched OFF.