Depends what alternator you have. Once you start putting additional loads on the charging circuit the alternators capacity can easily be overwhelmed. I have an 80 amp one but some 90 etc has much lower amp alternators. The efi system alone probably uses 10 amps , my electric fans about 20. Add a few lights then spots/ cb/ fridge/ stereo and suddelny you are taking more out than is being produced. Start winching at night if you want to see what your car is capable of!