If the lamp is normal, then do the following: connect two wires to the pluses (contacts) battery, and connect their other ends to the lamp contact. It does not matter how the wires on the lamp are connected. One wire is connected to the lamp body, and the other to its contact. If the lamp does not light up, replace it.
Attention: It is necessary to be sure that the contacts on the lamp and in its socket are not corroded. Clean contacts if necessary.
If the lamp is working, then insert it into place and turn it on. If the lamp does not light up, then check the voltage supply using a test lamp. To do this, one wire of the test lamp must be attached to a good ground or directly to the negative battery terminal. The other wire of the test lamp must be connected to the voltage supply plug or wire. If the control lamp lights up, and the main lamp still does not light up, then the connection of the lamp with «weight». To check this, attach a wire «masses» to the lamp holder. She should be on fire.
Note: Some lamps have only one contact for voltage supply (e.g. for parking or indoor lighting). These lamps are connected to «weight» directly through your body.
If there is no voltage on the wire going to the lamp, i.e. the control lamp does not light up, then the switch is most likely faulty. Check for a contact on the switch.