IVECO 7.5t are 24v as a rule.
DAF 7.5t are fitted with the hella plug 12v system just below the radio by your left leg.
I must admit that I have had the same problem of the plug melting but you can pick up spare leads for about £3.00 or I can for my WAECO at least.
sorry people i should have said its an 18 tonner sleeper im in this weekend, are the sockets on the left hand side of the console , sort of pointing in to the passengers foot well?
just been looking at a 12v/230v 24ltr coolbox
gooutdoors.co.uk/5709388003300
took the coool box back to makro and exchanged it. not a problem as i will be using it in the hella socket from now on, as long as it fits. if not it will be in the big fridge at the back along with the pallets! 
cheers for the help people 