2002 ducato (motorhome) 2.8jtd

Hi there,
Horn hasnt been working since i got it.
Had a look this evening and there are 2 wires going to a relay which drives the horn.
A black/white and a red/green

The black/white is a switched earth and the red/green should be live.
The switched earth is working fine but there is no power @ the red/green.
I traced it back under the cab and couldnt get continuity between it and under the hood...however there is no power on that cable in the cab either so maybe im on the wrong cable under the cab...anyone know if there is more than one red/green cable in the loom??
Or if there is a usual suspect when it comes to the horn?

I ran a fused cable from the batt to the red/green under the bonnet and it worked fine but i dont want it to become a permanent fixture.

Tomorrow ill see if i can get under the fuse board and find the cable there.
Cheers,
Marty.

I'd be tempted to run a wire (as you did) from a battery or ignition supply aslong as you put a in-line fuse in it.

You said 2 wires going to relay...do you mean the relay windings?

Cheers,
Yeah there are 2 wires going to the relay...a switched neutral and a live (which unfortunately aint live!)...the live is then switched @ the relay when it energises.(the horn has its own ground)
However as the live aint live then there is neither a live supply to the relay to energise it or resultantly to the horn.

WOuld anyone know if the wiring colours change as they move through the loom?...or would it be fair to say they retain their colours?
Cheers,
Marty.

Yes, it would be fair to say they retain their colours. But they can change at some significant junction (sw. or fuse etc).
Without a diagram and colour codes it can be painstaking tracing what goes where. On the rear fog lights on my older model (see below) there is an inline fuse which took some finding!
On my way to my MOT test this week I saw someone I knew and attempted to pip my horn - nothing! How could I have forgot to check the horn? With a length of wire from a nearby skip luckily, I managed to sort it out before the MOT!
Then it failed on the rear brakes... grrr.
good luck with your horn!
cheers
lwm
ps. does it really need to be operated by the relay though?

Ran a fused wire for a finish..think the relay may have been part of an alarm that was at some point removed
marty