Looking at your pic you can see why your having trouble because very little air would be hitting the rad. Is it possible to put the rad up front or another downsize the cooler ? Everything is tight looking at that and somehow you need to make space so the rad can get the cold air it needs otherwise you will never stop the overheating problems and it could kill your engine if it not sorted.
Your fans must have been working overtime trying to cool the rad and the standard wires for it would get hot after a long time of running so it then melts. Another option is to run the fan on a switch inside the car but using the correct wire and relay so that you dont have the problem again.
I have fitted a few switches to big bhp cars over the years and never had a problem doing it this way aslong as you remember to flick the switch when the temp starts going up. Only down side to this is the noise when your doing 20 mph along the sea front with your arm on the window....... lol