As far as I am aware, you require an SBig Relay Adapter Box between the mount and the guide cable, unfortunately, you may have already damaged the wiring if it has gotten hot.
The relay box electrically isolates the mount, see here:
http://www.astrovid.com/technical_do...y%20Issues.pdf
Specifically mentions the SBig ST5c just over half way down.
Also, are you running the latest version of CCDOPS and have you downloaded the latest SBIG Drivers.
Cheers
John G