seatbelt audible warning fault

[gutterburner]

Hi im new to this,so bear with me,I have a 56 plate 1.6 hdi berlingo desire which has developed a fault with the seatbelt audible warning, the warning goes on even with the belt plugged in but goes off after about two miles although the warning light stays on. Now this is also connected to the wipers,ie if I need to use the wipers then the audible warning comes on again and will go off after the two miles. The local dealer has done a diagnostic check which he says is inconclusive, but it may be the bsi computer, I am unwilling to spend £200.00 plus for a bsi computor which may not sort the problem.
Any help would be much appreciated
Gutterburner