Hi Roy ,
Have a read from the link below !
http://www.skywatcher.com/downloads.php?cat=20
Take the power cord off the mount and using a multimeter check the voltage at the pins that plug into the mount you should get around 12 to 13.5 v you should not get more than that with the car not running .
To do this test plug the power lead into the car cig lighter socket at the other end that goes into the mount use the multi meter to check the voltage on the 2 pins (you may need someone to hold the plug while you check the voltage on the plug pins).
But I think it may have something to do with the firmware as per the skywatcher website link above.
Have you got Firmware version 3.35 on your SynScan hand controller ?