Wiring Harness Confusion

Sheesh, I'm getting ready to put a new 50 2-stroke on, and will be going with an analog tach. I've identified the binnacle, key switch, tach and control cable part numbers, but I give up on the harness.

I keep seeing "optional" primary engine harness, and the word "optional" is throwing a curve at me. What 16' harness do I need for a 704 binnacle, 704 single key switch, and analog tach (6Y7-83540)? I was told the engine harness had the tach wiring built in, but I've seen so much contradictary information I'm losing my mind!

Any help would be most appreciated!

[boats.net]

6X3-8258A-00-00 16ft 10 pin Main Harness(engine to key switch harness)
6Y5-83553-N0-00 Gauge Power harness, key switch to gauge.
Not is all you will need unless the analog tach has oil warning lights in it, then you will need 6Y5-83653-00-00 Trim/Oil Harness for 2005 and newer motors.