Horn ec300

[mgre2643]

Hello just trying to sort the last thing on my 2002 ec300 before I can get it moted.

I'm.having problems with the horn it just isnt up to scratch i tested with a multimeter and I'm.getting 5 volts going to the horn when the switch is applied I would of thought this should be 12volts ??

There was also a box that I thought it would of been a relay that was fitted before the horn but I have tried a relay but doesnt work as I believe you need another power source for the relay ??

Picture of the box below if any one can tell me what that box is so I can get another would be good trying to get oem gas gas parts isnt that easy in the UK so an alternative would be good ??

Any help appreciated

Matt