I think that one could be the vacuum lead to the unit with a red line and no description in my picture below.
Do you see the grey hose just in the lower left hand corner of that picture entering the unit? Look and see if yours belongs there..
What is that unit called? Ignition control (wild guessing)?
Cap'n...while looking around there. Can you see if you have a loose 3rd wire next to that hood-switch in the picture? Or let me know how your 3 wires are connected if there are no loose ones. I believe they all are brown/brown-something... thanks!