One of the biggest problems of the humble 6v system, is that people dont know how to look after it well, and i think thats a very big reason why people have the opinion of them being 'weak' etc. But i think, if there are strange people here like me who want to stick to 6v for no logical reason, then read on. I hope my experiences will help others who have less experience with electrics to have a safer, better car without switching to 12v.
When running at night, everything adds up. You have to remember that at 6v:
a) everything takes twice the current of 12v
b) bulbs are not as efficient because of the properties of filament wire used, so they have to be higher wattage to be as bright as the equivalent 12v wattage
c) losses are higher, because current is higher and voltage is lower, resistance of wires, contacts, fuses, switches etc plays a much bigger part in messing up how the system works.
But it is very easy to fix it, and especially if your car has an old wiring system that hasnt been touched much, like most of these 6v cars have i guess.
You will need:
Wet and dry or emery cloth
Silicone based contact grease (not normal grease or vaseline!). Its expensive, but you dont need that much. You will find it at your local auto parts store, and especially motorbike parts store.
Thats basically it!
All you do is, start from somewhere, and disconnect every connection, clean it with the wet and dry, apply some contact grease, and reconnect it. I would do one connection at a time if you dont know the vw wiring system inside out, if you disconnect, clean and reconnect one at a time, thers no way you can go wrong.
General tips:
Remember the headlight earths on the inner wings at the front. Take the screws out, and clean the terminal itself, AND the patch of inner wing thats directly under it, to bare metal. Also clean up the screw. Cover the patch of metal, the screw, and the terminal, with the contact grease, and reassemble. On the one side, its awkward because sometimes the earth screw is right next to the fuel filler, so you cannot get to it with a screwdriver, you need a screwdriver bit in a ratchet socket driver, for example, or a flexible screwdriver drive.
Remember the fuses! Clean up the fuse holders, completely to shiny bare metal, and also roll some wet and dry into a tube and poke it through the hole in the fuse holder, as thats where most of the contact is. Also clean up the bases of the fuses with the wet and dry too. Cover with contact grease and put fuses back in.
If you are feeling bored, remember the terminal where the battery and main power cable connect to the starter motor.
For spade connectors, make sure you clean the male spade to bare metal, but also that you clean the inside of the female spade. This can be fiddly, but you can do it with folded up wet and dry.
Once you do this, you may find that your 6v system works better, and once more, since you applied the contact grease, it will protect it for a very long time, so it would be unnecessary to ever do this again probably.
So...thats it! Hope its useful to someone.