It's an all original, mostly rust free car with about 80,000 kilometers. I purchased it for the price of the paperwork to transfer the title over two years ago and I haven't done anything to it since, with the exception of more or less looking for a cheap 6 volt battery to get it going. That didn't happen; the part of me that wants to keep it original lost the battle to the part of me that wants to drive it and I decided to convert it it to 12 volt.
So what's involved in this swap? First you need all the parts. This is when you're glad you have a parts car gracefully rusting in your backyard. Upon closer inspection of the parts car you will undoubtedly also be glad you have a tetanus booster shot.
I've owned this 1974 Renault 4 since 2006. It ran quite rough, overheated constantly and it's much rustier than photos make it out to be so I parked it when the started died.
Here are some of the parts pulled from the 12v 1974 that you'll need for the swap:
The voltage regulator, the coil, the condenser, two headlight bulbs, the only two remaining tail light bulbs and the generator. Other items not pictured are the front turn signal bulbs, the wiper motor (dead on both the 1974 and the 1969), the instrument cluster lights and obviously a 12v battery. Note that you do not need the 12v starter; the 6v one holds up fine, it just spins faster. The wiring and the switches carry over as well.
First step is to remove all the old 6v bulbs and replace them with 12v ones. Clean out dirty sockets while you're at it, too.
Next step, remove the generator. Before you disconnect anything pay attention to which wire goes where! Take a picture, draw a diagram, whatever helps you get it right when you put the 12v one on. On a Renault 4 of this vintage you need to remove the fan and the fan pulley to get out the bolt that holds the generator to its mount. The fan is held on by four 13mm bolts mating it to the shaft on the water pump and a 17mm bolt that holds the whole assembly on. Remove those, remove the 17mm bolt that holds the generator in place, remove the belt and remove the generator. It's good practice to have a new belt to put back on.
With the generator out (see picture above) you can easily get to the coil and the condenser. Remove and replace (fairly straightforward.)
Next up is the voltage regulator. On a Renault 4 it's held on by two 8mm bolts on either side. Like for the generator, take a picture or draw a diagram to remember what goes where.
Once everything is back together it should look like this:
Everything works fine.. sort of. It won't fire, I'll look into why in the next few days (it may need new points.)