I used a comment on product 10256 to wire it. Comment is below.
Looking at this picture going clockwise starting at the very top left:
The headlight’s negative lead
The headlight’s positive lead
Your supply voltage (The voltage/current your headlight needs)
Gnd
And Arduino IO pin
1 and 4 are connected through the mosfet. Connectivity between those two pins is controlled by 5.
2 and 3 are connected together directly, so they could be omitted.
I don't get whats wrong with 10256 (you wired it up wrong?). Also make sure you have a resistor on the arduino-gate line so you don't draw to much current and fry your arduino.
It looks like the same part, so you shouldn't see a difference. What kind of "trouble"? Is the LED/fan always full-on or full-off?
This is a "wild guess", but I wonder if the resistor on the assembly helps prevent damage from static discharge, and the loose part is getting "zapped" during handling?
If the parts are dying for no apparent reason (not over-voltage, over-current, or over-heating), static discharge is a likely cause.
Once the resistor is "permanently" connected to the MOSFET, that would provide some static discharge protection.