Connect devices to relay
How it's done
During testing we just follow LED on relay module.
In this case we use water and air pumps, both work on 5-12V. Because of this we choose 9V power source.
There is one trick. When we power Arduino 2.1mm power plug there is one pin with same voltage we can easily use - Pin Vin.
We will use power source from Vin pin for pumps. Connect Vin Pin from Arduino with middle pin on relay channel one. We can use this middle channel pin to connect with second channel, because they use same power source.
Then connect positive pin from water pump with relay channel 1 pin. Choose that one which is not powered if is not driven by module.
Orange wire on picture is power source from Vin (9V if we use 9V power source for Arduino). We make bridge for the same power source from one to another relay channel with white wire. Red wire from device is connected to relay channel pins to be turned on when relay channel is turned on too.
Ground wires from both pumps connect with any ground Pin on Arduino.