Ah fair do's ive not used the ones from autobulbs direct, but normally if you put bog standard LED bulbs in a Mk2 or 2b sidelights you get the bulb failure warning light up.
They only draw less that 1w compared to the 5w of a normal filament 501 bulb. Normally it sets it off, but obviously not in this case.
Alan
EDIT: its no biggie if it does anyway, just fit one of these each side.
http://www.autobulbsdirect.co.uk/led-resistor