On a 2005 LR3 HSE, the electrical reference states that it is an integral part of the central junction box (CJB). I only see three relays attached to the it and none of them is for the horn.
Horn went on continuously while driving and only stopped when fuse burned out. Replacing fuse just burns itself out. Wire circuitry from horn switch to CJB indicates no short circuit. However, from horn to CJB does. Disconnecting at CJB the connector leading to the horn removes the short circuit condition. This tells me short is in the CJB. Replacing it sounds costly. Less costly alternative is to bypass with new relay circuitry, but alarm will not have a horn to use.
Horn went on continuously while driving and only stopped when fuse burned out. Replacing fuse just burns itself out. Wire circuitry from horn switch to CJB indicates no short circuit. However, from horn to CJB does. Disconnecting at CJB the connector leading to the horn removes the short circuit condition. This tells me short is in the CJB. Replacing it sounds costly. Less costly alternative is to bypass with new relay circuitry, but alarm will not have a horn to use.