mac solenoid wiring

I'm passing with a confusing phenomena with my mac i give it a +12v switched and tested it with a gnd it doesn't work when i give it a direct +12v and test on the same gnd it works so i bring my multi meter and tested the voltage in the +12 switch and it was about 11.6 testes the mac again and it doesn't run when turning on ignition the wire gives 13.5v and it doesn't work also I'm confused

i changed the place of the +12v switch and it worked thanks