Many others will have had the problem with the horn ring on Amazons becomin intermittant and pressing the horn results in a strangled squark rather than a manly honk! This is because the horn contact rim is silver plated and silver corrodes (or gets burnt off by the current gulps from the horn sounders). I cured mine by adding a relay. This means that the horn ring only has to supply the relay coil current rather than amps. To do this I did the following: 1. In the engine bay cut the black wire that comes down the steering shaft (and is switched to ground by the horn ring). The end that comes from the shaft is then connected to one of the relay's coil terminals. 2. The other coil terminal needs +12V. I took my supply from the brown wire that supplies +12V to the horn sounder - you can use a piggy-back spade connector. 3. The other end of the black wire that you cut (which goes to the horn sounder) is connected to a normally open contact on the relay. 4. Finally, connect the other side of the normally open contact to ground. Diagram attached. You will now have a much clearer and steady honk (assuming that the sounders were OK in the first place).

Mike, that's very useful - many thanks! :)

will any relay do? 

What relay did you use?

Boggo four-terminal relay from any motor parts shop, except Halfrods, because they're crap and don't stock them.

I used a very old FIAM relay from my junk box (I realise that this is not exactly helpful). Any basic normally-open relay that will take about 5 amps will do.

I'd recommend a rating somewhat more than 5 amps. Horns can suck a fair bit of current. Standard car relays start at 30 amps so no problem there.