Electric short on Citroen C15 Van?

Have a real headache here. 1999 Citroen C15D RHD 1769cc van. On journey, suddenly van loses all power and rolls to halt on country road. Try starting it , nothing!.

Lift bonnet, check cables to battery, fry my fingers. Realise positive battery feed wire has come up against sharp bodywork and has earthed it. Disconnect battery quickly as lead is very hot. No other signs of problems.
Replace battery, nothing, buy new battery, replace it , nothing.

Recover vehicle to home. Strip ignition switch and rebuild, still nothing. Replace starter motor and solenoid with new unit, nothing. Follow the electric chain and replace pre-heater solenoid with another unit ( they are like hen's teeth to find second hand),but still nothing. Turn the key the first click, red battery lights ignite on dash, second click no preheater lights ignite, third click , sort of click and buzz from pre-heater relay. Running out of options. No sign of burning on any connection or brown staining, all fuses o.k. (at least the eight on the bulkhead are fine) Any help would be appreciated. Many Thanks,Mike