HERE Gps unit dual

Hi I have pixhawk cube which I’m trying to run 2 gps units which are here gps 2 an original gps pixhawk 2.1 gps unit I have main connect into gps 1 an 2 into gps 2 port which modified cable when I switch the pixhawk on both lights flash on gps unit it doesn’t get gps lock then afterwhile both gps units shut down can anyone offer any advice thanks.