The problem is solved, looks like my father in law never had a tune up done on the boat, the in-line fuel filter and the water separator were due up. Changed both and replaced the 5 amp fuse for a 3 amp one. Went for a ride with an amp meter connected between the fuse and the low pressure pump. I had reading of 0.96 amp.
Everything works great now, back to original state and power
Anyone could tell me were i could get the manual for the engine ?
A 5amp fuse is still a low fuse and shouldd not cause wires to melt.
Keep on looking for the trouble. Unplug all connections on this wire, apply dielectric grease or silicon spray on all connections. It could be the unit this fuse powers that is at fault.
If the 5amp fuse blows it's time to stop boating until U sort it out.
The part i was looking for is the low pressure pump. It is still working tho I will start by changing the fuel filter (wich has never been changed) then, will put back a 3 amp fuse and test again. If not, time to look further into it