I like the on off to the throttle linkage idea
A micro switch would be good I think.
If there is a lot of on and offing going on, the main relay should really be a solid state one. Relays with button style contacts aren't really meant to be repeatedly turned on and off all the time. It pits the contacts and some times after a while they arc and weld shut.
Glen
Mother Nature educates all of us that are teachable. She's hardest on the ones who refuse to learn. Punishment is automatic, immediate, and without pity.