Setting timing

[SoCalSlaughter]

Ive been trying to set the timing on my 90' Suburban for about an hour now, Ive read on many forums to disconnect the "Set timing" wire, but I cant find the right location, some say next to the ecm behind glove box, some say by steering shaft and some say next to distributor. Ive set the timing to 0 and reconnected both wires behind glove box and by steering shaft, and the truck seems to have had lost alot of power and throttle responce. Idle isnt very steady, goes between 700-900. Any ideas? Thanks!!