Curious speedo activity

[semmyroundel]

I'll probably be told that 'it's a thing' but wondered why if I pressed the horn on my 2011 Nightster, the speed apparently drops by about 20%.
Clearly the speed doesn't, but the speedo thinks it does.

 

[Paul P.]

I will be watching this question as my '03XLH speedo reacts to other actions as well...

 

[watchman]

Sounds like an earth problem

 

[semmyroundel]

Sounds like an earth problem

If it is, could there be repercussions?

 

[softail898]

If it is, could there be repercussions?

Not if it is an Earth for the Speedo alone. If is shared with other stuff, Rev Counter, Fuel Guage etc. then those will be affected.

 

[watchman]

Check the main earth to the engine there are 2 points one horizontal stud for the main loom coming out of the primary next to the starter motor and one about 3 inches away vertical from engine cases and takes the battery negative lead this one plays up as it corrodes between the threaded stud and the aluminium case due to water running across the case undo clean em both up and the studs too to make good contact that should sort it also being a 2011 bike rubber mounted under the swing arm pivot there is a braided earth strap from the cases to the frame utilising the stabiliser link bolts pop them and clean and redo this should eliminate the problem
worst case the starter starts to twat about due to bad earthing just done them last week on my sporty build and redoing the isolator rubbers on it a 2004 bike

 

[semmyroundel]

Check the main earth to the engine there are 2 points one horizontal stud for the main loom coming out of the primary next to the starter motor and one about 3 inches away vertical from engine cases and takes the battery negative lead this one plays up as it corrodes between the threaded stud and the aluminium case due to water running across the case undo clean em both up and the studs too to make good contact that should sort it also being a 2011 bike rubber mounted under the swing arm pivot there is a braided earth strap from the cases to the frame utilising the stabiliser link bolts pop them and clean and redo this should eliminate the problem
worst case the starter starts to twat about due to bad earthing just done them last week on my sporty build and redoing the isolator rubbers on it a 2004 bike

Will do, thanks.

 

[spakey]

Worth checking the regulator output. A simple check is to measure the voltage at the battery while running, fast idle should be about 13.5v, rev the engine and it should not go over 14.8v. If it's not within that range you may need to investigate further.