I guess that when they did it the first time, all they did was clean
up the contacts on the rear of the horn push (air bag). Since then
Peugeot has come out with a solution. Take off the air bag and there
is the earth for the horn just pushed in to a square hole. I reckon it
only needs slight corrosion and the horn becomes intermittent and then
does not work. The connector has to be cut off and the two wires
crimped into a ring terminal. Use a self tapper to screw it straight
into the aluminium boss. Just below the square hole there is a
slightly raised bit about 5mm in diameter. Drill there, all the way
through. It is best to remove the steering wheel but can be done in
situ if care is taken not to damage the switch gear behind. Use a self
tapper just long enough to go through the hole. Put everything back
together and the horn should work with no further trouble.