Cleaning should do the trick. It may go out again tho. My friends 01 police road king has same problem. He just cleans it off every time.

 

What lube is he using in his transmission? I just turned 74,000 and have had no trouble. The magnetic drain plug seems to catch all the contamination that is generated. The "high dollar" gear lubes seem to guard against speed sensor contamination by generating less metal particles.

 

Just did this and it was the sensor. 30 minute fix. $60 part.

 

BTW - you will need to remove the battery to get to the cable socket.