Overheating

My Volvo 2004s40 overheated and my machanic replaced the head gasket.I was told after that I needed a engine wiring harness. Then the car overheated again and he replaced the coolant resivor.4days later the car overhears again. The car seemed like it wasn't getting power upon accelerating about 3weeks after the head gasket repair. He said it was the engine harness. What is the problem as I have several thousand dollars on this car. The engine harness is to expensive I feel he should have told me about the engine harness befor I repaired the head gasket as the problem of over heating is not solved. If in replace the engine harness I will be spending over 5 thousand on these two repairs alone. What do you think?Have been taken by my mechanic?If I knew the harness needed replaced I would have never went ahead with the head gasket. Also he said the block was not cracked since it is still overheating could the repair on the headgasked be failing or cracked?