Horn not working - nor is replacement

[v8rumbler]

My 6v horn goes pop when I press the button and pop again when I release the button. Bought a replacement - which does the same.
I put a volt meter in the cables and when button is not pressed it shows 0.4v and when it is pressed 5.8. these figs were with the engine not running.

HELP

[Bolder]

Have you tried adjusting the little screw at the back of the horn .
Hope this helps
Colin