This lets you replace the weak 3V incandescent bulb from a free headlight with a much brighter 9 LED array from a free flashlight. Both free items from Harbor Freight.
The battery pack retrofits 3 AAA batteries into the 2 AA battery compartment of the free headlamp. I used tin foil to make the contacts and it works well for me. This brings the voltage to the pins in the light housing to 4.5V.
The housing adapter holds the LED array from the free flashlight. You'll have to pop the led array out of the flashlight by taking the battery pack out and pushing the array out through the end with some sockets and some light hammering.
Press the reflector into the adapter in the orientation you want.
You'll also have to solder some wires to the + and - of the LED array. Then plug those wires into the pins of the housing, and close it up. Pictures for reference.
Coupons below. You may have to make two trips to harbor freight for multiple free items, it depends on the store.
If those links expire, then I'm sure they'll have new ones, these things have been free for as long as I can remember.