[Moppie]

Wow, new harness into a TR6 should be fun.
Putting a new harness into a car is one thing Iv never done, but I would lay it our completely, making sure everything is labeled first (not that there is that much to it, being a 73 TR6).

Then make sure everything in the car that needs to be out, is out. Carpet, seats, rubber gromets in firewall etc.

Then find the start point. My best guess would be fuse box, or somewhere under dash, and work your way out from there.