I think its telling you to cut and abandon the existing brake wire from the brake light switch to each of the brake lights. It gets replaced by the two wires from the signal switch. If you don't remove that wire, then both brake lights will flash when either left or right turn signal is selected.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.