I don't agree with Bob's analysis since it is clear that he doesn't know which way the plunger of the contactor is moving relative to the vertical axis of an airplane if the brackets are mounted flush to a firewall ( In this configuration, the plunger could never be aligned with the longitudinal axis).
He also mentions looking at hundreds of T.C. aircraft...... I wonder how many of them were approved to purposely be experiencing 6+ g's during flight on a regular basis.
The contactors are mounted at 45* on the RV-14 because it is convenient for structural reasons and that then largely takes care of any possible issue as a result of pos. or neg G's.
BTW, there is nothing wrong with mounting the start contactor with the plunger vertical as long as you know which way the plunger moves, you mount it so it can only be influenced by neg. G's, and then you avoid high neg G's (likely 99.9% of all RV owners do).