On my 1999 Acura RL, changed the left front turn signal bulb going through the wheel well-major pain, fixed the fast-flash problem for left blinker. But the original bulb tested good, both filaments. so figured it was some sort of contact problem in the socket. Tried to replace the right one (also bad) major P in the B, air intake pipe right where you need to snake your arm in to get to the socket which wouldn't budge. Gave up after hand & arm getting too scratched up. Resorted to old school: gave the front-right headlight/lamp assembly a good rap with a wooden mallet. Right turn signal now good! (at least for now -- until socket contacts go flakey again)