It's hard to say which type of bulb is used in your speedo and tach. 1980 was right around the time Yamaha started changing over from the twist-lock BA9S bulbs to the wedge style T10. You'll just have to take one out and see. Easiest to check would be the ones in the center console. You can just remove the cover with a couple of screws. There will probably be 5 bulbs in the instruments - 2 in each one for illumination and a 3rd in the tach for the high beam indicator.