Most recommend it to be on the negative side but having it way back at the battery is not what I would do. It needs to be easy to get to not under the floor. I would use something like this one;
https://www.snydersantiqueauto.com/P...earchByKeyword
and mount on the firewall so it can be reached from inside. On the Model A's we mount them under the drivers seat or close to that area where it is easy to reach thru the open door.
Also see the replies on the A forum;
https://www.fordbarn.com/forum/showthread.php?t=274231