Any suggestions on how to switch a negative 12V 3A supply with an Arduino? Low cost so preferably not a relay! Thanks.

 

Welcome to AAC!

Any suggestions on how to switch a negative 12V 3A supply with an Arduino?

As in on or off? Use a suitable MOSFET; P channel or N channel.

 

+5V is the supply for the computer.
-12V is the supply for the load.
R1 is the load.
"in" goes to a IO pin on the computer.
Then "in" is not connected or below 0.5V, Q2 is off.
When "in" is at 3 to 5V, Q1 and Q2 are on.

 

Thanks very much. Won't be able to try it out for a few days but looks good!