In case I need to commute home after dark on my electric bike, I added a front headlight (5 watt MR11 halogen) and a rear tail light (Red LED tail light for “off-road” use). The front headlight enclosure was designed to be used on a bike, and included a nice mounting bracket and enough cord that I could harvest some to run to the rear tail light. Black zip-ties hold the wires to the frame. The rear tail light had no enclosure, so I soldered the wire directly to it and epoxied it into the back of my rear rack. Both lights run off of only one of the 12v batteries through a 5A blade fuse and an automotive switch mounted under the battery pack.
If you look at the picture of the tail light you can see that it is sitting between the two solar panels hinged on the rear rack, but those are another story.
Total cost, under $15.

Front Headlight: $5.65
Rear LED: $2.75
Switch: $1.52
Blade Fuse Holder: $1.27
5A blade fuse: $0.60
Zip Ties: $2.79