Light comes on when turning on parking or headlights.All bulbs are burning but want blink when turn signal is engaged.Truck lights works fine and power is coming through plug end.Any ideas why trailer light isn't blinking??

Is it a two stage light with three wires coming out of it?
Can you take a multimeter and check the voltage when the signal is on?
Does the other side work?
Does it work when the flashers are on?

some leds dont draw enough to flash, have to get a different flasher sometimes

sounds like a bad groud, same thing happened to me.

dos it get brighter when you hit the brakes? if not then that leg of the circuit is not working. It will be the green and yellow wires. They do brake lights and turn signals....check there...and as CSCinc mentioned some LED's dont have the proper resistance to trigger the flasher the proper way and will give you a signal of a fast blinker like you have a bulb burnt out...you would need to switch the flasher relay.