Normally when the relay fries every time, the problem is the fan itself, which is drawing too much current. It is a good practice to change both relay and fan at the same time.
However, if you want to hardwire it, just measure the existing fan wire and use the same gauge.
JEEP Grand Cherokee 4.7 Lmtd 2004
HID 8000K in low and fog / Quad Squad member
KYB Gas-a-Just shocks / Pirelli Scorpion ATR 245/65/17 - Transgo reprogramming shiftkit.