There is a reason the map lights do not light up with stock set up.
The trace carrying current from the pin to the FET measures 1mm wide. The calculator here shows that a 1mm trace can support well more than 2.5 amps (about 16 actually). So it looks like the FET's 30W rating is the limiting factor. The existing 12V8WAL bulbs are unknown wattage, though. Presumably 8W? With 2 on the original circuit, each would have to be 15W or less to not exceed the FET's power rating. But if they are indeed 8W, then the maps lights added would give a total of 32W, slightly exceeding the stock FET's rating.
(not my work, full work up click link)
http://www.subaruforester.org/vbulletin/f85/body-inegrated-unit-dome-dimming-circuit-data-repair-83167/