How to wire emergency vehicle lights for fire trucks, police cars, ambulances, etc.
Know your laws. Before installing lights on a vehicle, make sure you have permission to use them. This is regulated by the state in some areas, and local jurisdictions in other areas. Using emergency lights without permission is a crime!
Get your equipment. Purchase the right type of light for your needs. Determine the size, mounting location and power-type (wired or plug-in) of the lights you want. www.galls.com has many great light choices.
Route your wires. Look at the type of light to determine how to route your power wires. If it is a plug-in cigarette lighter type light, route the cord around your windshield/dashboard so it does not obstruct your view. Plug it in/switch it on as necessary.
If it is an internal-power unit, run your wires through the trim, dashboard or outside through the window and hood to avoid unsightly wires and potential electric shock. Your wires will need to go to the unit from the control board, to the battery. Connect your control board (switch panel) directly to the battery, and make sure the wire to the battery goes through the firewall securely.
Ground and cleanup. Hide any loose wires under trim in your car. Always ground your lights/switchboard with a separate wire, hooked to the chassis of your vehicle. Test your lights, and make sure to switch them off to avoid draining the battery. Run your vehicle when possible, to keep the battery charged. Make sure to secure the wire to the battery, so it does not come loose.
You take full responsibility for the wiring and ownership of your lights. Do not do anything illegal or unsafe. It is your responsibility to ensure that you comply with all applicable laws, rules, department guidelines and recommendations.