Like Bob C said, most of these aftermarket wire harness are made for a 30-31 stoplight switch mounted to the backside of the crossmember. Therefore the wires did not need to be as long as they would be needed for the 28-29 transmission mounted brake light switch. I've been told Sacramento Vintage made the correct harness for a 28-29, not sure if they still do. Give them a call. Or splice in some green wires to lengthen the wires to the brake light switch. That's what I did. You can but the wire from some of the vendors or Toms Engine Barn has it.
https://enginebarn.myshopify.com/ Cloth covered primary wire.