From MopedWiki

CEV headlights come on virtually all vintage mopeds. A good majority of them are a sealed-beam type bulb that eventually burns out from vibration, or most commonly, a voltage spike when the lights are switched on while the engine is running above idle.
The bulbs that have a metal backing can be modded to accept cheap and easily replaceable automotive type bulbs. To do this you'll need:

• A steel-backed CEV headlight bulb
• Angle grinder, a drill motor with a grinding or cutting wheel chucked in, a Dremel, or a hacksaw if you ghetto
• Soldering iron
• SINGLE terminal 'trailer bulb socket' from a car parts place
• 6 volt 18 watt bulb for Puch, 6v21w for other makes, or #1157 (12v 21w) for 12 volt systems
• Clean rag or paper towel

1. Slice the nub straight off with your grinding or cutting tool
2. Enlarge the hole enough for the new bulb to pass through
3. Solder the black wire where the 'hot' leads go to the harness (you may need to bridge the High & Low beam wires). Make sure the ground goes to the bulb socket
4. Shake out all the debris from the old bulb and wipe out the inside with the paper towel
5. Install the bulb, clip in the socket and button it up!