Hello John, i can't find this wire on any of the schematics, so looks like it may have been added. I wonder if it's a ballast bypass, from the starter? Has your starter been replaced with one, i think a 59X starter, that has a separate output for a bypass wire?
You can check if you get 12V+ve on the wire when cranking. If that's what it's for and you still need the bypass, then it's connected to the +ve terminal of the coil, but please make certain that's what it's for before you connect it
There was also a bypass relay option, which used a +ve from the standard starter, but that required a 12V relay, and the contacts were used to bridge the ballast, i assume you don't have any additional relays that you can't account for?
If you decide you don't need to connect it, make sure it's well insulated and safe or disconnected both ends if you can find the source
