Hello Pierre.
I'm not sure what year your B7100 is.
When I stop the engine on my B7100 it states to pull the throttle lever back completely until the engine stops and than turn the key off,and never use the key to shut off the engine.
If you are having problem shutting the engine off check the throttle linkage.
Also when shutting of the engine, bring the engine rpm down to a slow idle.
By the sounds you don't have a wiring problem.
If you should need the basic infomation maybe I could help for I have a B7100HST,an there others on the forum with alot more knowledge than I.
How the weather over there in France?
Take care and stay safe.
Thomas..NH