Need International 9200 repair help

Hi,

I have and early '94 (almost '93) International 9200 with a broken speedometer. I have changed the probe at the rear of my Spicer transmission to no avail. There is another probe there too which connects into wiring going forward. The probe I believe to be the speedo probe is wired into a box marked "idle boss" and then that harness goes forward toward the engine and instruments. Am I correct which probe is which and what in the world does the idle boss do? I cannot find it on any schematics.

Thanks, any insight is appreciated!

Fred