Reassemble the toolhead as shown observing the following:
Take care to not pinch any wires when installing the new heatsink assemlby.
The fan duct must be installed before the two bottom fasteners can be installed.
The red ground wire goes thought the heatsink fins and on the bottom right fastener.
The fan must be up on the heatsink before the fan duct is installed so that the wires are routed correctly.
The short fastener goes in the bottom left hole.
Both heater pins go with the latch facing outwards.
The heater and thermistor wire pairs are not polarized.
For more details, see the Assembly OHAI