Which 2 pins do I connect
Using pins in the diagnostic ports of the OBDi system, which was on GM vehicles 1995 and older. You just plug in an OBDii code scanner in the port under the dash. You can pick one up for around $20 or a generic one or have an auto part store scan the truck for free.
Use an OBD2 code reader. The old method is for OBD1 cars.