You need the correct electrical schematic for that exact model tractor and either a test light or an ohm meter and basic automotive electrical knowledge.

Lacking either usually results in a more complicated problem and ultimately a more costly repair.

Sears lists two manuals for the 917.270840... here is the schematic from one manual but it may not be the correct one for your tractor.

Perhaps it would be more prudent for you to post what problem you're having and we might point you to the right place to start diagnostics.

Note in the schematic above, that there's a "Truth Table" on the lower left of the page.
That shows what connections should or should NOT be made in the different key positions.

Thanks, I think I figured it out.

Thank you for sharing your findings with the forum.
That's how this works.