Agreed. Practicality wise bad earths are responsible for a lot of vehicle electrics. Trouble is when you stick electricerry in a vehicles a whole new world of hurts opens up. My first suggestion is to go over the control system from generator back to batteries and check the voltage at every connection and joint. Bloody tedious but can show up some bizarre problems. The problem is the voltage drops. Therefore bulb or whatever tries to compensate by taking more amperage, it only 'Knows' it wants to do the work. As the gadget can't cope with extra ampage it blows. For explanation to anyone whose baffled, Think of ampage as the amount of current, IE a gallon, not exact because an Amp is 1 Coulomb per second. If you want the definition of a Coulomb ask 'cause you really don't need it. Voltage is the pressure, say lbs per sq inch. throw a gallon of water over someone it will get them wet. Shove it through a pressure injector at 2000lbs per sq inch you can strip paint. If an Amp at 1 volt runs through a resistance of 1 ohm you get 1 watt of power. Haynes do a very good manual on auto electrics. Mechanically electrics on a vehicle are not difficult, you just need to know a few basic. Every one should carry a cheap multi meter its as important as a spanner. When God made electricity he didn't let us see it. having read it again. The extra ampage, is like trying to force more water through a pipe then it can take and bursts. I realise this is a ramble, but my physics teacher was a genius he got me to understand, I'm not.