40mA is typical for a single "conventional" LED but a "high power" LED could draw more. 40ma at 12 volts will be less than a half watt of power drain, not ten watts, although perhaps that is supposed to be one LED "equal to" a 10 watt conventional bulb. (I don't think it would be bright enough though.)
With LEDs you have one extra hazard, if the maker has not provided reverse voltage protection, it is possible that hooking one up backwards would incinerate it--very quickly. I'd do any testing at a lower voltage level or check with the maker if in doubt.
How the fixture will behave will depend on what protections and what other circuitry they have built into it, I'd be hesitant to suggest it could "just" be tested as if it were a plain LED alone. You might want to confirm with Aqua Signal directly to find out what their suggestion is, the odds are you aren't the first guy to have this problem.