Im trying to help a friend sort out why a relay on her car keeps blowing.

It feeds windows, radio, indicators, dash, etc and it occasionally blows and seems to melt a bit of the plastic relay holder.

Im trying to work out what would cause it to go that severely. Its not taking out any fuses (all circuits fuse protected) which surprises me as there must be some big current draw or a loose connector sparking?? thought automotive relays would be fairly robust to a simple loose connectors.

I intend to do obvious connector check, check earth check current drawn by each circuit in turn etc, but it would be useful to know what would cause a relay to blow like that??