I had to change a fusable link in my 85 but it has been several years. I do believe the fusable link is in a labeled black box with other electrical fuses on the passenger side of the car ahead of the battery. The fusable link has a box shape to it and when you pull it out you can see if it's gone or not by the broken link.
I must warn, it has been a few years - I could be wrong and I don't have my Z handy to compare.
What symptoms are you having? Mine sounds like it was doing near what yours is doing and it was the fusable link.