I hate cutting or splicing wires, but if I recall correctly, I used a Posi-Tap connector on each of the pos/neg wires going to the brake light. They're pretty clever, and minimally invasive, just putting a small pinhole in the wire insulation. Sort of hard to find these days in hardware stores, but Amazon has them.
Ran the wires to the GS100A flasher, then to the TruFlex wires. Being LEDs, they draw such little power that I didn't bother running separate fuses for them, and they work fine on all of my bikes.
https://www.amazon.com/Posi-Tap-14-16-Ch...r=8-5&th=1
Here's the GS100A flasher.
[url=https://www.amazon.com/Podoy-GS-100A-Controller-Flasher-12V-24V/dp/B01F4OKWSG]https://www.amazon.com/Podoy-GS-100A-Controller-Flasher-12V-24V/dp/B01F4OKWSG