If you want the 2 wire LED's to go completely on/off and be useful as turn signal and running lights, you will need 2 diode bridges, 2 - 10W, 10 Ohm resistors, and 1 - 20W, 10 Ohm resistor (ignore the wattage ratings on the schematic). This high power solution doesn't require a flasher fix unless the rear lamps are replaced with LED's too.
Here is the theory of operation for this modification which is only used if you are running a 2-wire LED module:
Resistors R1 and R2 provide a low impedance ground path to the floating turn signal and running light wiring after the lamps have been removed from the original circuits.
Diodes D1-D4 form a bridge circuit and control the current flow through the LED module which is developed by turning on the running lights and/or turn signal. Diodes D1-D4 are shown as discreet components but they can also be purchased as a single monolithic device - see picture below.
If you look at the image of the monolithic device above, and my schematic, you will notice terminals marked as: +, -, and 2 ~ (AC).
Connect the left or right turn signal wire (tan or grey) to one of the diodes middle ~ pins and then connect the running light wire (black/yellow) to the other middle ~ pin. You will also need to connect one end of each the power resistors to the junction/connection point made at each of the diodes ~ and wire connections. The other side of each resistor is then tied to ground through the black wire. Now connect the LED module's + wire to the diodes + pin and the LED's - wire to the diodes - pin. One turn signal/running light modification is now complete. Perform the same steps for the other side...
When the running lights are off, R1 provides a ground path for the turn signals. When the turn signal is turned on, R2 sees the full 13.7 VDC across it and dissipates about 9.69 watts. The 13.7 VDC is also applied to diode D1 which controls the current path through the LED module and through diode D4 and R1. R1 will have a very small voltage developed across since the current will primarily be controlled by the LED module. When the turn signal is off, the LED module sees an effective ground potential on each side and will be off.
When the running lights are turned on, R2 provides a ground path for the running lights. Resistor R1 sees the full 13.7 VDC across it and dissipates about 18.77 watts. The 13.7 VDC is also applied to diode D3 which controls the current path through the LED module and through D2 and R2. R2 will have a very small voltage developed across it since the current is limited by the diodes and LED module. When the turn signal is turned on, D2 and D4 both become reverse biased and will stop current flow through the LED module - the LED module turns off which means the turn signals are working in conjunction with the running lights. Resistor R2 sees 13.7 VDC across it during this condition and dissipates a high wattage again.
I have a design that is very low power (less than 100 mW) and works very well, but it requires transistors, zener diodes, and a few resistors. Maybe someday I will produce it if there is a big enough market...