European turn signals use only a single wire to power their lights while US turn signals use 2 wires. When you to go install your European turn signals on a US car you are faced with a dilemma. Do you use just one wire to power the European turn signal or do we modify the European turn signal to accept both wires. The answer is you modify the turn signal to use both wires!
Trying to use only one of the US wires to power the European indicators doesn't work because the flasher relay that runs the indicator is load sensitive and one wire wont pull enough load to make the indicators "blink" correctly.
There are multiple solutions which include using a Uhual Tap-a-light (NLA) or drilling a hole and mounting a second light bulb in the bracket. However a simpler solution exists. There are double filament adapters that fit into single filament holes and add the double filament and double wiring needed.
For about $4 you will be able to plug in the correct US bulb and wire the bulb to US spec.
Although the adapters squeeze right into place, i did add some epoxy to hold them in place. Be careful though, the body of the adapter must make metal on metal contact with the bulb holder as this the electrical ground for the light circuit. Adding a dedicated ground wire is also not a bad idea since the light, by default, grounds through the body screws by making contact with the brass rivets holding the light assembly together.
As you can also see i broke off and removed the spring loaded filament contact as it is no longer needed and just gets in the way.