You say two units are brand new. Were the other two already in the garage and did they work?
What else is on the circuit with the lights?
The current draw for them should not be a problem but depending on what else is on the cicuit they could be overloading the cicuit. All of the plugs are probably on the same circuit.
Unplug all but one and try it. Or take it into the house and try it.
Let us know so we can provide more help.