The National Luna Ignition Sensor Cable is an optional accessory for the DC Power Packs. It plugs directly into the Ignition Sense Port located on the face of the Power Pack. The Ignition Sense Port allows the Power Pack to support vehicles where the charge voltage drops very low or is very erratic. This may be the case in some vehicles with "Smart Alternators". Plug the small end of the override cable into the Ignition Sense Port. Plug the larger end into a socket that provides a positive voltage only when the ignition of the vehicle is on. CAUTION! - Connecting the ignition override to a permanent 12V source may result in excessive discharge of the main battery. Only use the Ignition Sense feature if the vehicle alternator voltage is below 13.2V under normal conditions.