BC547 transistors biasing
a BC547 is a NPN transistor and requires biasing on its base,I assume your going to have 12vDC in the car,the usual biasing for switching is 560 ohm 1 watt resistor the BC series of transistors are pretty hardy,if you feel the transistor, while on load and it gets a bit to hot, I suggest a shunt resistor at the collector,trial and error is required here,but when the transistor remains just warm on load it should be ok.a schematic diagram would be a help to answer you properly.