Its been a while since I did this so I need a refresher. My 66 already has the HEI conversion harness in the engine bay. I'm replacing my under the dash harness that includes the fuse box. Do I need to replace the pink wire that comes from the ignition switch or is that one ok? Or Is it just the hei engine harness that I already have replaced that needs to be changed?

Oh man... :(
I just did this about a year ago. I replaced front light, engine, and dash harnesses in my '66 wagon, purchased from M&H. I had them do the HEI and internal regulator conversions at the same time.
I do remember receiving instructions with the dash harness having me relocate or install a large pink wire that ran from the fuse box to the ignition switch. Seems to me like it had to be located at a different position on the ign switch plug.

I don't remember the exact details that were included with the harness. :confused: Maybe I can locate those instructions...

I also suggest calling the harness manufacturer and asking.