vw caravelle cuts out

Hi, Have got a 1997 vw caravelle 2.5 tdi, which randomly cuts out, may happen twice on a journey or not at all, seems to be linked with the glow plug light flashing after it has cut out. Have had it plugged into a vw computer and reports engine wiring harness fault, also some clever bod seemed to think it was the fuel pump which wasn't so had that reeplaced which wasn't either. Any ideas?
Cheers Mat