i normaly use 0.35mm or 0.5mm ( much smaller ) it's not like sensors for gadgues draw much current.
if there recating to revs i'd say the more likely fluctuating due to voltage, check your grounds and ground locations ( engine block is best ) other than that check your bat tvolatge is relativly constant as the revs rise ( shouldn't affect quality gadges tho as they should have internal regs )