Six volt batteries can be a real pain in every part to charge. Mine wouldn't charge on the mains so I lost my temper stuck it on the vehicle jumped with twelve volts and left the engine running. Charged up perfectley and holds charge. I am assuming you know if the vehicle is positive or negative earth. So as suggested just either use a single 12 volt, or jump start and leave the vehicle running Whilst it is running check voltages with multimeter. A Dynamo should give about 13.2 to 13.6 volts. DON'T try reading amps, most multi meters won't cope with the ampage and will melt (Literally) . Clicking solinoids can mean a flat batery, OR one of the connections to the battery terminals is loose or dirty. Check all the battery leads are tight, including the connection from battery to starter motor. If that is dirty or loose, won't go!