berlingo horn not working

[Bunyip71]

Hello I wonder if anyone can help with advice please.
I have a 04 berlingo1.9d with no horn.
When I bought the van there wasn't a horn fitted and the plug from the loom to the missing horn was badly corroded.
I put new connector on the loom and bought a secondhand working horn but nothing.
According to the wiring diagram the feed comes from the battery to a fuse named 'C' in the engine fuse box. I can't find any info as to what fuse 'C' is and there is nothing marked on the box. Then the feed goes onto fuse F7 in the compartment fuse box. Fuse F7 is live with the ignition on but goes dead about 30 seconds after I turn off the ignition.
I think I've traced the wire to the back of the com 2000 unit but it's dead all the time. Does any of this sound familiar to anyone? Is there a way I could bypass all this polarva? If anyone can share their knowledge on the subject I'd be very grateful.

[brodfather11]

I think there is references to the horn being earthed through the steering column.
one way was a jubilee clip on the column lower down near the floor with a earth wire attached and wired to a self tapping screw in the body .

Going off after 30 secs is normal "to save your battery".

There is some fuses under the tray in the engine fuse box. lift the top fuses out and the maxi fuses should be underneath

[geoff]

  31-HU1tvymL._SX38_SY50_CR,0,0,38,50_.jpg (Size: 561 bytes / Downloads: 50)
  31-HU1tvymL._SX38_SY50_CR,0,0,38,50_.jpg (Size: 561 bytes / Downloads: 50)     If you cannot get a result and just want a work around then run a wire from the battery to a switch mounted on the dash somewhere then run the wire down to the horn then back to battery.

On another car with a wrecked steering lock / combined ignition and starter switch I used a bakelite light switch for the ignition circuit and a single gang light switch for the starter circuit, it worked really well.

Not suggesting you use the above switches as others will be more elegant !

[RattyCortina]

There are a few threads on here re: earthing the steering column, I found I had to earth the moving section so rigged up a 'brush' arrangement with a small braided earth strap an spring.

[Bunyip71]

Thanks for the advice folks much appreciated.
I've been working on it today and found the live feed for the horn (white wire) to the back of the com unit it dead.
Also the flat wired horn feed that goes through the wheel has had a sharp stuck in it at some point and had torn into the wire.
The earth to the wheel from the loom has continuaty but the live feed to the horn itself is dead.
I can probably get the wires on the com 2000 unit replaced but no idea where to start looking regarding the dead feed to the com 2000.
The L7 fuse in the compartment fuse box is live so I'm guessing something has cut the wire from the fuse box to the com 2000 connector.