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