I bought an '86 FJ1200 this year and over the course of the season I had 3 or 4 instances where my battery went dead on me.  I to was told that my battery & starter are in good shape.  I believe there is a short in the electrical system.  Every time I used the handlebar lock my tail & marker lights came on.  No big deal, I am taking it apart this winter to paint it at which time I will go over the entire electrical system.  Our bikes are 20+ years old we have to expect things like this to happen.