the Chev factory wiring diagram [VIEW A] shows what I've seen on every 55-59 foot start I've dealt with ... note that "start" and "ign 2" are the same terminal .... the V8 wiring is
here, with an actual seperate "start" terminal - violet [from the starter] still goes to the ign terminal, which is only hot with the key on
Rasman - put an ohmmeter to your switch and see which terminals connect when the key is on, the wire from the starter must go thru the switch or some mechanic is gonna be getting a hell of a surprise some day when 'bumping' the starter to get the BB in sight .... never seen a switch on these trucks that only has 3 terminals - maybe Chev cheaped out in 59 and used GMC parts?

Bill