1995 Yukon Timing Setting

Hello to all.
My question is this. What is the proper way to set the timing on a 1995 GMC Yukon with a 350. The emission sticker says to unplug the single white wire to put it in bypass mode. I am use to seeing this on the "traditional" HEI ignition. But on this one the connectors are on the bottom of the distributor. There is one connector with four wires (which the sticker says not to remove. The is another connector with two wires, one of which is white. I tried that one and the truck would not start, so I "set" the timing with all connectors hooked up. Now the truck is lacking power. I had it set at 5 degrees b4. Failed smog checks (oh yes, I am in Cali) "functionality" test. Also had to replace the EGR valve because of high "N O" readings.
As always, any info is greatly appreciated.
Thank you in advance
Chuck
Any information, as always, is greatly appreciated

On my 90, the wire to disconnect is under the black cover on the passenger firewall. I have heard that on some models, this wire is under the glove box. The wire is either black with a tan strip or tan with a black strip. It will be a single wire.

With it disconnected, the timing should be set to zero.

//2000CAYukon