okay, searched lots of posts, lots of schematics. The rpm sensor signal is tapped by several components, such as the a/c control relay, cluster, diagnostic connector, but do not go through it. If I am reading the schamtic right, the rpm sensor feeds the idle speed / EGR control unit which has an rpm output (green / yellow) sent off to various components, such as diagnostic connector pin 1. This is a single wire output. I am assuming I check this to ground? pin 2.

obviously with test lead extentions, hood closed, driving, etc.