LED bulbs don't draw enough current to make the old style flashers work (bi-metal strip that heats up because of the current running through it). On my 58 2-ton, I replaced all of the bulbs with LED except the bulbs in the turn signals on top of the front fenders. Those bulbs draw enough current to make the old flasher work fine. I did not want LEDs up there because the front lens is amber and rear lens is red. LED bulbs need to be the same color as the lens they are behind or they are not very bright (I believe it is the narrow color spectrum of light they put out).
