help please

[LA240sx]

hey im new to the forum. I have a 98 240 and im trying to find the hole in the fire wall so i can run some gauges but i cant find it anywhere. Also, i tried hooking up my a/f gauge and i found three wires running off of the o2 sensor which comes off the header-2 white and one black. I tried one of the white wires and the gauge worked but everytime i used my power window it went to lean and it never left stoich besides that (it acted like a voltmeter). so i decided to try the other white wire and now the gauge doesnt work at all. If anyone could help me i would greatly appreciate it.