Had a problem once while riding an 850 Mk2 Commando.
The bike spends a lot of time laid up and it had a chronic brake fluid leak. The brake fluid caused some grunge and corrosion to occur on the button switchs, particularly the kill switch. During a ride I went to touch/check the kill switch and it worked fine but would not close again so I was dead in the water until I sorted it out and cleaned it.
The reason I bring this up is to see if there's any suggestion as to what (if anything) should be used on the contacts. At first I thought dielectric grease would be a good idea but not sure this is a good idea for the kill switch contacts.