64 Dart Rewire
The other thing "I guess" you could do is use isolation diodes
Buy something like these:
https://www.amazon.com/dp/B007Z7OQ5G/?tag=fabo03-20
And obtain a SPST (two terminal) switch of your choice
and wire like:
Hot source.............fuse.........to switch......to flasher...........
On the output side of the flasher, connect the anode side of three diodes. The remaining lead of each diode (the cathode side, the one with the bar marking on the diode) will then connect to the brake wire, the left front, and the right front. You of course will need to protect them, heat shrink, etc.
EDIT I guess you don't need one of the diodes. Here is the same circuit applied to a motorcycle. In this case you would need to connect the brake switch wire to the flasher that is grey
