It should show you a wiring diagram in the back of the manual, if not, check here, do a search for service manuals, and you will get an idea. If it is in that kind of condition, you have to expect to spend a little money on it, it not going to repair or replace worn parts on its own.
It may be easier to buy a complete wiring harness, and CDI if the wires are that far gone. I have seen wiring harnesses on ebay for that model sell for about $10 or less. Just keep an eye out on there if you think you need one.
THE 80's RAGE! Currently owns:
81, 85 Yamaha Tri Moto 125
83 Yamaha Tri Moto 200 x2
82,83 Yamaha Tri Moto 175 project
85 Yamaha Tri Z 250
84 Kawasaki Tecate 250
84 Honda ATC 70
85 Honda ATC 350X
84 Honda ATC 250R
(2) 84 Honda ATC 200x
82, 83 Honda ATC 185s
81 ATC 200
Lots of other parts and bikes