need help plz!!!!

[dohdoh806]

OK so heres the run down the other day i was lookin at my fuse box...i know u fig out already but heres the thing ok i have a 1998 240 wit a silvia s15 swap now lights always worked fine...but the other day the left side wouldnt turn on so i checked fuses, blown but the thing was that it had 15s but the box read for 20s ok so i fig y not put those wrong cuz az soon as i hit the gas it burned out more then once...so i tried 25s nope,stupid ?ion is should i just run the 15s or trace my wires cuz of course it worked fine before but then again y did it burn out period...