Battery cut-off switch. FIA approved. Most race sanctioning bodies require the use of this special (diode protection device) cut out allowing the switching off whilst the engine is running without damaging the electrics. The switch has to be accessible from inside and outside the car; the external trigger should be located on the windshield scuttle panel, preferably on the driver's side. It should be clearly marked by a red flash in a white-edged blue triangle. This switch, mounted accessibly, can do the job; or mount it less accessibly and it's an anti-theft device. Comes with instructions that tell you how to use it to interrupt the battery ground. If mounted in a locked boot or other secure space it should deter even experienced thieves when you use it.