According to my reprint copy of the service manual only 2 terminals are used on the 49 switch.
Use an ohm meter to determine which 2 have continuity when the key is on and lose it when the key is off. It won't matter which side of the switch is hot. It just goes in and out.

"It's just a phase. He'll grow out of it." Mama, 1964

1956 Chevy 1/2-ton 3100
1953 Chevy 6100 "The Yard dog"
1954 GMC Suburban Now with a new proud owner.