Legos are fun, but they miss real lights. Fortunately for us, Lego holes have nice dimensions, which fit nicely with standard LED dimensions (3mm or 5mm).
Here is a guide on how to light a Lego police truck for less than $5.
Step 1: Hardware Setup
You will need LEDs (very cheap), an old IDE ribbon cable, an old Camera battery, and a breakable tulip socket (also very cheap).
Break the IDE ribbon to form 2-wires cables. Also break the socket into 2-pins blocks. If you need to make the connector go through a Lego 5mm hole, also break the two pins individually.
Step 2: Soldering
With a soldering iron, you can now create cables with LEDs on one side and a male connector on the other side (don't forget to add a resistor on one of the pins). Mark the - wire with a black pen.
Then, create the battery connector and solder one or more female socket on each side. In my example I have one connector on the front and two on the rear (for a blinking roof light, still not functional). Again, mark the - connector with a black pen.
Step 3: Correctly Integrate in the Truck
My battery fits inside a 6x4 Lego block. This white Lego block will maintain the battery just at the right position !
Step 4: Enjoy !
Step 5: Re-use Your LEDs in Other Situations
Wires and LEDs can be reused in any other thing you build. For example, as lightning for a crane !