The electrical lights were hand made by boys. Electric cable, bulbs and bulb holders/shades used to come from the market and those were assembled at home. The bulbs were connected in a series using a single cable, the ends of which used to go in the socket. One single fused bulb meant the entire string won't work. To increase the lives of strings, a master bulb would be added at one end which would break the flow of current when heated and created blinking lights.
In the late 90s such strings were not made at home but were bought from local electricians. Still later, in the late 90s and early 2000, cheap electric lights, also known as Christmas Lights in the west, imported from China were widely available. This is where we are now. We buy them and use them on Diwali.
However, this is also changing and the next emerging trend is to call an electrician and get him to do the Diwali lights for you. The electrician brings his own lights, puts them up and after Diwali takes them down as well - complete outsourcing.
The disadvantage though is that you can't figure out if the decoration is for Diwali or for a wedding.