Thanks for the input, Pink.
Another source for a harness is American Auto / Marine Wiring, http://www.customwiring.com. They have a harness specifically for the MIGI, as well as for a number of other TD replicas and kit cars. I may eventually buy a complete harness, but first I would like to assess how much of the old wiring is bad. I’d also like to figure out what caused the original damage — which happened before I got the car — so that I don’t fry some more wiring.
By the way, I scored a MIGI assembly manual last night on e-Bay. I’m hoping it will provide what I need.