For those who have hooked these up, which wire is the signal wire (coming off the o2 sensor) that I hook the purple wire (from the guage) to? Also, do I hook this up the the first o2 sensor or the secondary one?

 

if this is the gauge from autometer it is a narrow band af ratio gauge. It will go narrow band o2 sensor I believe it is the first one in the exhaust stream (someone correct me if I am wrong). Your install will be cleaner if you find out what pin corresponds to that sensor's input to the ecu, this is the way I hooked it up on my EG.

 

Tap into the wire going to the ECU.