No, it's not a cable and resistor issue. The computer in the new bike controls the blinkers. The Euro bikes don't have a resistor to function. It's handled by the computer.
In theory, a very cheap resistor could likely be spliced in line and probably fix the issue, but a resistor is nothing more than something turning the electricity into heat. It's old tech. Recent BMWs do have the ability to fix the issue of the lamp warning via the computer update, but the software hasn't been made available for the GSW yet. It's nothing more than changing the option in the computer.
'15 KTM 500 EXC / '13 BMW 1200 GSW / '05 Honda ST1300 / '04 Husqvarna TE510