A multi-meter is essential, in my opinion. They're not expensive and they take the guess work out of solving electrical problems.
TrueA 12v lightbulb on a couple of bits of wire is a damn site cheaper.
My dad looked at me and went "Congratulations - you've invented a torch". (Digression over)
HiCheck voltage at stalk. Check continuity at stalk. Check voltage at horn. Check continuuity (to earth) at horn.
There's not much more to it, to be honest. If there's 12v at the stalk switch, but not at the horn, you've got a broken wire.
ThanksIntruder Alert - Watch out lads we have a /\/\/\/\/\ freelander /\/\/\/\/\/\ in the defender section - turn out the guard!!
Guy, probably worth popping over to the Freelander forum and asking over there (which is here). Us defender owners don't aspire to high tech systems like having horn buttons on your steering wheel! While we could have a good guess others over on the other side may be of more help.
Oh and welcome, hope to see you over here once you progress to a defender![]()