Immobiliser/alarm on 306 XTDT

[seanandde]

Wondering if anyone can help please. My partner has an old (1994) 306 XTDT. The alarm wiring is, we believe, faulty as the siren sounds, sometimes for a few seconds, sometimes continually, randomly whether parked up or being driven. The key/alarm fob does not work and neither does the central locking. We found the key operated switch behind the front headlight which should disable the alarm but it doesn't work. The only way to prevent it occasionally driving the neighbours round the bend and him jumping out bed at all hours to try and sort it is to disconnect the battery... did that again last night and now it's immobilised itself

To be honest, the car is heap but we rely heavily on it for work as we're rural. Is there any way we can, once and for all, somehow fairly simply disable the alarm without spending a fortune (which we don't have!)? Spoke to the local garage who service/MOT it but they "won't touch anything electrical/alarm related" I was told.

Any help or advice much appreciated, thanks.