The "Throttle" button is only used to increase the idle speed. Normally it is not used. It helps when manually cranking the engine to start it. That is also the only time the spark button is used. It is necessary to reduce the spark advance to keep the engine from firing backwards (breaking bones?) when using the starting crank handle.

Is your 1929 Pickup a 1 1/2 ton or 1/2 ton? Chevrolet did not build a 1/2 ton pickup in 1929.

Thanks.  This is good info.  The 29 is being delivered on tuesday.  Its taken an extra week for delivery because others have been flooding the truck which then that transporter could not get onto his transport (no winch).  Finally, I got a transporter with a winch.  And its extremely cold where its stored.  Only the owner, who passed, could start it.  My original thoughts, before your reply, was, I have a choke button (standard expectation), a throttle cable from pedal to carb, so I thought it might have been a manual cruise control when needed.  I'm glad you replied.  Being an estate sale, I'm still chasing a title and BOS.  Will update the truck data on tuesday.

Gary, You might find the throttle cable handy when the truck is loaded and you are at a stop on a hill.  It will make things a little easer using the hand throttle when starting off from a stop not having to jump off the brake to the throttle on the floor.  Good luck with your new toy.