Bongo Fury

I have been having problems with my glow plug relay unit ( I think??) basically my glow plugs were first replaced due to white smoke when starting, but once they were changed it then would start but not catch, so my mechanic assumed my glow plug relay unit had blown due to my glow plugs previously not working so new relay was put in and has lasted around two weeks .It seems to have blown again. Is there some underlying problem which could cause this as I dont want to have to keep replacing relay.

See if the wrong length of plugs were fitted - the bus bar will short out on the pipes! You can add washers to shim it out of the way or bend the pipes.

are you sure its the glow plug relay and not the fusable link?, its inline fuse behind the starter battery that goes the glow plug relay?

check to see if you're getting voltage at the glowplug busbar when the key is turned, that'll give an idea of what's doing what or not.