When checking voltage at the switch, remember that you’ll have to pick up a 12v ground from another source to hold on your voltage meter ground because the hot wire is cut and then joined by the switch itself. In other words, there is no ground on a 12v switch being that the 12v hot is being passed thru the switch to the light.
At the light, one of the 2 wires to the light is a ground and is a good place to check voltage.