350 TBI,1990,engine timing

I need to set the timing on this engine, it is in a GMC suburban, a mechanic friend told me to disconnect a male / female plug near the distributor or the back of the valve cover on driver side to disable the advance signal from the electronic timing control device, he said the wire would be tan with a black tracer, no such wire that I can find, the only wire with a disconnect is a purple one, way down behind the cover where I can only touch it with my fingertips, anyone have more precise info on this procedure ??, thanks:(

check behind the relay cover on the pass side firewall. it will be a black cover that comes off with 2 or 3 plastic nuts. behind it will be a single wire with the connector hes talking about. i thought it was brown but i may be wrong. anyhow, im pretty sure its the only single wire connector behind there.
run the truck to opperating temp. loosen the dist hold down. unplug the single connector. set timing to specs, i believe 0 on that. tighten the dist. retest timing and make sure it didnt move on you when tightening the dist, adjust if need be. plug the connector back in. put the cover back on and your ready to rock and roll!

bob

1990 & 1991, some models did not have the tan-blk connector. What you did was put it in limp mode by jumping the ALDL connector under the dash ( like you are retrieving codes ). The underhood decal should say which it is, whether EST unplug or Grounding ALDL.