Hi, as far as I know the horn is independant to everything else, its fuse and realy are both in the engine compartment fuse box:
Fuse number F1.7 (blue 15A), Relay K33.

If this fuse is OK, then get someone to press the horn switch whilst you listen for a click from the relay, if it clicks, suspect the horn is faulty. If it dosent click, or the fuse is blown then another wiring fault may be present [including any of the following, bad earth to horn, bad earth or connection on horn switch(via airbag rotary connector), wiring short /open circuit between cab to fuse box and fuse box to horn, internal wiirng fault between fuse and relay].
As for indicators, as stated earlier not all vans had alarms, so if your doors lock / unlock ok with remote, i'd personally leave well alone! if security is an issue, have an aftermarket alarm fitted.
Hope this is of some help,
Regards,
Andy