It's a voltage regulator for the gauges, the indicator lights are straight 12 volt, the gauges thinking 5 volt. If the copper on the contact points for light sockets is dull looking, take a rough pencil eraser and erase the contact area to a bright copper color, that cleans it up to carry power, often lights will then work. Do the same to the contacts on the bulb socket. They oxidize and then quit working and common. You can slightly bend the socket contacts out further to make firmer contact too.