yeah, i've done the install on an e36 with an autometer guage (which probably doesn't matter, but just in case it does). on the back of the guage you will have three wires, a 12V power wire, a ground wire and a signal wire. you attach the 12V power wire to your ignition wire, but to the one which reads 12V only after the ignition switch is in position #2, not before, my wire was green. then you attach the ground wire to any ground (just a steel nut, not painted). then run the signal wire through the firewall and down to the O2 sensor, you will want to connect it to the wire reading 0.5V when the engine is running. this wire for me was black.
it's not a very hard install, you'll find it easy, good luck.
p.s. -*** after you have installed it and want to see if it works, and it won't right away, give it around 15 seconds to warm up (it has got to warm up). if you see nothing happen after 30 seconds and your reving it a little bit, you did it wrong.