Help with Glowshift boost gauge install...

[ST_Bo]

I have a 2018 fiesta st I'm trying to install a glowshift boost gauge I just don't no where to connect everything for the constant power I had it fuse tapped into the horn for ignition source I had it fused tapped into the radio for ground I connected it to the ground in the headlight switch and headlight source I had it plugged into a purple an white wire of the headlight switch I think the ground or headlight source switch is where I'm having the problem I'm clueless with cars but I love my fiesta and I want to do everything my self with this car and learn along the way any help would be appreciated