Do you have the mouse enabled for Tron? If you are using command line MAME, then in the .ini it should say: mouse 1 (not mouse 0)
If you are using Mame32, then you need to right-click on TRON in the GUI and make sure the MOUSE box is checked.
If you've done all that, and it still doesn't work, have you tried hitting the TAB key once Tron is running to map the controls?