Pretty straight forward. From the pointy end towards the cable:
Contact 2: Earphones, Positive
Contact 4: Earphones, Ground
You might need an amplifier in between.
If you google around for U-174 or U-94 wiring, -plug, or -jack you'll probably find some stuff. If you have a DC headset they already come with a complete wiring diagram in the box; that might help, too.