(ET) pack not isolated from frame??

[Dave & Debbie Barden <daveb seanet com>]

I was working on my modified E15 (?) today, and while loosening a 
connection on 
one the cable connections I grounded to the body with the wrench and got 
an 
ugly juicy spark.  That doubly surprised me because I am always careful 
around 
battery terminals and potential grounds but also because I thought that if 
the 
pack was not grounded to the frame you wouldn't/shouldn't get current 
flow??  

So what gives here am I under a mis-impression and showing my ignorance or 
do I 
have a ground somewhere that I shouldn't have??

Also since this tractor has been modified by the previous owner I don't 
really 
know what model it is.  My E12S has the PTO plug up front on the left.  
This 
one has the PTO plug down by my right foot.  Would this be an E15 or E20 
or???

thanks much,
dave
Seattle
E12S
E?? modified