I have a G8C forced air furnace with a diagnostic indicator saying the limit switch is open (4 blinks). If I am looking at the circuit board diagram correctly it looks like the limit switch is a little red dual on/off switch in the upper left corner of the circuit board. The other switch appears to be the pressure switch, which is on. What looks like the Limit switch is off.

I am not sure this is right and don't want to just flip what I think is the Limit Switch back on, unless I'm sure.

Anyone know?

I think the manufacturer is York.

The high limit is a 2 by 3 black rectangle pastic with 2 wires going to it. It will be located to the right just above the heat burner box

Is it just a thin plastic plate, below the burners? It's about the size you said, and it's held in place by two screws. Dow do I close it?

That should be "how" do I close it?

Tape it with a screw driver take it out at flip the end with your finger.