starter relay-clutch safety switch

There's only so many places the problem can be. The "functional path" of the start circuit is.........

Dedicated "start" contact at igntion switch...........column connector..........bulkhead connector...........to starter relay

If you are satisfied that you are actually losing power at the yellow wire at the relay, then that should eliminate the relay as a problem.

So either the column connector or the switch itself. ABODYJOE did a great write up on changing the ignition switch some time ago