I have a 05 Ford Fusion and the horn doesn't work. The horn will sound when you lock the doors with the remote but it will not work when you push on the centre of the steering wheel.

How can I fix this issue?

 

Generally the wire coming up the steering column has to make contact with a ground on the steering wheel itself. Either the wire coming up the column is open somewhere or the contact for the horn on the pad isn't making contact or there is a loss of ground connection at the steering wheel itself. Anything else would probably involve disassembling the pad on the sreering wheel and personally I wouldn't recommend getting in there without a good manual since you are dealing with the SIR system. (Supplemental Inflatable Restraint) ie , AIR BAG.