99 dodge dakota.5 speed...,my left turn signal blinks really fast.

REMOVE ALL bulbs , test wires/circuit for HIGH resistance(Corrosion or partially broken/damaged wire) Make sure you have correct bulbs!! Swap them from the other side (that IS working correctly) to aid in verifying parts being good. NEVER assume by the looks! Turn on hazards and see if any one of the bulbs looks a little different than the others , that also may help narrow down the problem area.