How about a more quick and dirty method? Plug in an electric heater, or something else that draws a lot of power, in your garage. Turn it up to max, and then turn on your garage door opener. If nothing happens, your plants will be fine. If you trip the breaker, try plugging in something else that more closely approximates the draw of your lights and try it again. At the very least you will trip the breaker and probably learn where the breaker box is after looking into getting it reset.