I believe this issue has been posted before on other Star forums, but since this is a fairly common issue (dirty and burned contacts, keeping the switch from working right or at all) and since I just repaired another one this weekend, I figured it was worth posting again as a good idea for winter maintenance and repair, especially on older bikes.
Note: I buy, sell and repair (many) bikes for fun and profit, and have repaired many starter buttons and switches in my time, and they are all very easy and basically the same. There is generally no excuse to buy a new one unless they are truly broken, you have 10 thumbs or don't have a single Phillips head screw driver at your disposal. Yamaha doesn't service just the starter button switch separately either, they make you buy the whole assembly!
Step 1: loosen the front brake master cylinder on the right handle bar (2 Allen screws) and move it up the bars about an inch from the to give you room to work. Tighten it slightly in that position to keep it from flopping around while you work
Step 2: Loosen and remove the two Phillips screws on the rear of the starter switch housing and carefully separate
Step 3: Remove the small clip (small Phillips screw) that holds the wiring harness in position inside the housing, but leave the clip attached to the harness end zip-tie
Step 4: Remove the 2 Phillips screws inside the housing that hold the starter button assembly in place while looking straight down on the inner switch body. While holding the switch housing in that position, carefully lift the white starter button switch back up and out of the way.
Step 5. You will now see a conical spring that faces with the small end downward, making contact with the starter button. Carefully remove it and set it aside
Step 6. Push the starter button up and out of the housing
Step 7. You now have two contacts to clean, one on the back side of the starter button and one on the switch backing piece. Any blackness, corrosion, burn marks or residue left behind can cause the switch to malfunction. I have even found fried bugs in there! I usually start with some 000 grade (fine) steel wool and carefully work it across the contacts. If I am unable to get all ridges, grooves and imperfections removed from the contacts with steel wool, I then use a fine emery board and lightly sand the contacts flat and level with a few strokes. Blow the switch out well when done, and add a dab of dialectic (electrical) grease to the contacts to help prevent future corrosion.
Step 8. Reassembly is really just the reverse of the above, beginning with inserting the start button back into the housing. Adding a dab of dialectic grease on the starter button contact at this point will help hold the conical spring in place while you position the white starter button switch-back, and push down and screw it back in. Reattach the wiring harness hold clip to the inner switch housing using the small Phillips screw, and then close the switch assembly in the correct position over throttle tube while slowly bringing the two halves together with the outer housing Phillips screws. If the housing isn't closing completely, you may have a pinched or out of position wire-in which case, open the switch housing back up, re-position the wires try again. When done, check the switch for tightness and final positioning. Adjust as necessary. Don't forget to test the throttle tube for free movement. It shouldn't bind. Don't forget to move the master cylinder back down the bars into position, and tighten it back down.
On the bike I was repairing on this weekend, the entire starter button assembly (back, front, and conical spring) was missing, and the start button wires were cut off (as the prior owner installed a temporary start button), so I needed source another start button assembly to properly complete the job. Checking with my local dealer, the OEM switch assembly was $339, and they don't sell just the starter button switch separately. A quick search on eBay revealed a used right switch assembly with a broken kill switch from an 04' VStar 650 for just $12.00 shipped. Yep, the starter buttons are all the same-but the wiring wiring harnesses for the kill switches differ by model, making the actual button switches interchangeable on most star bikes. Since I didn't need the kill switch anyway (just the starter button switch), that one was just perfect for my needs! By disassembling the used switch housing from Ebay, removing the starter button assembly and clipping the wires off long enough to work with, cleaning it (as described above), installing it into my existing switch housing and then wiring it into the harness (using careful soldering and heat shrink tubing on those splices), I got a perfect result and saved $327 in part cost. Probably more like $3-400 (including labor) if I would have let the dealer replace the switch for me! This all took about 30 minutes total. Maybe I should start a niche business?!!!
-You need good lighting. Parts are small and easily dropped/lost
-Have some dialectic grease on hand. It helps to not only keep contacts clean, but hold parts in place during reassembly
-When removing and installing screws, a magnetic screwdriver is a huge plus
-Re-positioning the conical spring small side down on the starter button contact and reassembling the button switch can be a little fussy. Use the dialectic grease o hold it in place, take your time and relax.