I am new to this site, but I was thinking while reading this post...." I would not pay a bunch of money for a special Yamaha relay when I could make a $10.00 relay from an ole Chevy do the same job.  A relay is just a relay, a electrical switch."  I have repaired old boats with car parts when the boat parts could not be found (1970 Chrysler outboard).  Possibly a previous owner did something along the same lines to your Yammer?  But did a simi-crappy job installing and doing the conversion?  Anyway, I am glad you found the problem.    
If I have spoken blasphemy to the purest, I apologize .