power distribution for 3 pumps

Hi

i need a bit of assistance i have 3 pumps rated at 12v 3As each, i have connected them to a relay board for arduino.
the issue i am having is that i want to turn on all 3 pumps at the same time. my programming is ok and works as i have tested them with leds. i can turn on one pump at a time, but not all together. im guessing its a voltage and amps issue, but dont know how to solve it

if anyone can help that would be great thank you.

Quite probably. Unless you tell us all the actual details we're guessing wildly.