Electrical problem
1967 Chevy El Camino V8 Two Wheel Drive Automatic 130000 miles

My wipers quit working with no warning. The only way they'll engage is if I initiate the washer mode; that is if I push the washer button on the switch the wipers will work as long as I hold it.

I ran a volt test on the yellow, light bliue and dark blue wires to the wiring connections to the motor itself. I was told that all should be hot when ignition is on (no running) and wiper switch off. However, only the yellow connections are hot. All wires go through the same bulkhead connection, yellow to the fuse box and both light blue and dark blue as well as black wires go to the switch itself. Since the yellow wire is hot and others are not, I suspect the wiper switch itself and not the bulkhead connector.

Is there any way to confirm/deny this without dropping the dash and pulling the wiper switch itself?