Step one, take 4 way flasher out. Step 2 step on the brake, both brake lights should light. Step 3 turn on the 4 way flasher, step on the brake, both brake lights still should work. Step 4, with the flasher on, foot on the brake, signal left. The left brake light should go out, repeat for the right, it should also go out. If it all works like I've described, buy a HD flasher new, both of yours may be to weak to work as a turn signal flasher, been there done that...