replaced flashers with LEDs on 65 Mustang. Also flasher. Rear turns signals work fine but front signals flash at same time L or R

This problem could be in your turn signal switch.

All flashers worked fine before conversion to LED

Hum... have to think about that one. By flashers ( pleural) is there more than one now? Or do you mean one for turn and one for emergency?

Rear Land R work fine. But each time either one is on the front turn signals flash(both sides at same time). Thought it was new LED Flasher so changed that out; same thing. I would agree with you on turn signal switch but they worked fine before the LEDS. Checked all wires and ran good ground for flasher. It's got me.

I think.. maybe.. if you check power at the turn signal switch connector, what will you see? Can you disconnect one of the wires to the front signals and see if power is comeing from the switch or back feeding from the light. This is a stretch besause some leds have a diode in them and dont allow volts to pass through one way.. also when l have a elerical problem l sometimes make a schmatic to visially see where voltage comes and goes, remembering its like water in that it will flow to any path to ground it can.

Also the rear turns sometimes have a separate circuit to accommodate for the brake lights. Is this why they work fine? Hope some of this gets you thinking on a differant track to help you and me lol.. to figure this out.

Found It!!!. Apparently the front turn signals operate the dashboard turn signal indicator; and it's the only thing that's not LED on the system. So I thought that maybe it crossing current to the other light. Took it out and everything works perfectly. Thanks for everyone's time on this and maybe this answer will save someone else some frustration.

Glad you figured it out.

You were a great help. Telling me that the rear lights were on a separate circuit was huge. Thank You

Your welcome.. glad l could help.

So my apologies, but what fixed it? I am having the same problem.