On idea that comes to mind id it seems Harley has been having a problem with the rear brake light switch leaking, causing exactly what you describe, plus sometime fluid sprayed under pressure and smoking when sprayed on hot engine parts.
On the National Government recall site, there are several complaints about this:
http://www-odi.nhtsa.dot.gov/owners/SearchResults.actionA cut & paste of one complaint:
All Products Associated with this Complaint [img src="http://www-odi.nhtsa.dot.gov/owners/images/orange-up.png" alt="close">[/a>0 Associated Documents
- Crash:No
- Fire:Yes
- Number of Injuries:0
- Number of Deaths:0
Manufacturer: Harley-Davidson Motor Company
Vehicle Identification No. (VIN): 1HD1FR4189Y...
SUMMARY:TL* THE CONTACT OWNS A 2009 HARLEY DAVIDSON ROAD KING CLASSIC. THE CONTACT STATED THE REAR BRAKE LIGHT SWITCH MELTED DUE TO THE LIGHT BEING BUILT NEXT TO THE ENGINE EXHAUST SYSTEM. THE FAILURE ALSO CAUSED THE REAR BRAKES TO STOP WORKING. THE VEHICLE WAS NOT TAKEN TO THE DEALER, BUT THE MANUFACTURER WAS CONTACTED. THE VEHICLE WAS NOT REPAIRED. THE FAILURE AND CURRENT MILEAGE WAS 5,200.
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