I thought it would be good if we had a separate dedicated thread on this subject. The big Caravel thread is getting so long now (130 pages with posts stretching over a period of 3+ years) that you get prompted to consider starting a new one instead of adding posts there anyway, so here goes.
I can see a couple of reasons to why you should always consider rewiring of any used Caravel you buy.

1. Safety. You don't want an unsafe electric appliance in today's kitchens, there is so much wiring and electricity there now compared to in the 60's, and stuff that doesn't follow the standard tends to blow fuses and/or earth fault sensor circuits, or worse, give you nasty jolts or even screw up other equipment.
(BTW: Getting an IT->US or IT->EU adapter for an unsafe appliance does not make it safe! The Caravel I have rewired was not safe, but it was easy to make it safe.)
2. A simple rewire may sometimes make your previously electrically defunct machine work perfectly.
3. If you're going to change the heater because it was worn out or because you need one for 120V, you need to be able to make sure the rest of the wiring works anyway.
4. A Caravel that you can plug in to the mains is actually much more useful. I would like to say it can't really reach its full potential unless you can use the heater. Tried it with and without, and I think _with_ is much better.

Disclaimer: going inside any electric appliance and changing stuff without proper education is illegal in several countries. If you are not educated, you should always let a pro have a look at it before putting it into action.

But learning some simple rules is not forbidden, and I thought why not start there. After this, I'll follow up with some pictures of our Caravel. Won't be able to do that today.

About safety earth

The reason that most electrical appliances of today use plastic chassis is just as much a safety reason as it is a question of economics: if you double insulate by using an insulated chassis on the outside of an insulated wiring, you don't need to use an earth wire. And plastic is a great insulator. Metal... not so much.
All electric appliances need to adhere to the IEC rules for appliance classes, where you can see that our Caravels end up in class I. They have metal chassis, will be used in not-completely-dry environments, use a high voltage and thus need to use a safety earth connection. http://en.wikipedia.org/wiki/Appliance_classes

And, basically, this is it. When you connect the safety earth wire from the mains lead to the chassis, AND put the plug into a properly grounded outlet, you have a safe Caravel. Even if you would wire the rest all wrong, you're safe. All that can happen (aside from the fact that you might, in the worst-case scenario, also render the machine unusable) is that you will blow the fuse or earth fault breaker circuit, you will not get a live chassis.

On the other hand, it doesn't make any difference at all how well the Caravel works if it isn't properly grounded.

On my Caravel, the wiring was really OK, apart from that little safety wire not being connected on the inside. They simply cut the yel/grn wire off, instead of screwing it to the chassis, making it in effect a Class 0 appliance

Wikipedia's appliance classes article writer(-s) wrote:These appliances have no protective-earth connection and feature only a single level of insulation and were intended for use in dry areas. A single fault could cause an electric shock or other dangerous occurrence. Sales of these items have been banned in the UK since 1975.

You see what I mean? This Caravel was not only unsafe and potentially dangerous, it was also illegal. Just because some nitwit didn't connect all the wires way back when!
Meanwhile, the plug was a perfectly good, old, Italian plug with that cute earth pin inbetween the 0V/HV pins. It sure looked alright to me, so instead of being suspicious and looking at the inside, I cut it off and mounted a proper "swedish" safety-earth plug on the mains wire. Did that help? No, it made the problem worse! Now the machine had electricity in it, and... Yes indeed, a live chassis. It... tingled.

After having that look inside the chassis, I simply disconnected the entire plug and mains wire and replaced it with a new safety-earth (three-wire) plug+cable of the type that works in my country, this time connecting the yel/grn wire to the chassis connection point.

Done, machine safe.

This was not enough, however, to make the machine work. It did for a while, but then one of the kitchen fuses started blowing. all. the. time. Plug the machine in - BANG!

The reason was a worn out heater element. We'll get to that when the pictures are taken

I am sure there are lots of people here that have been through electrical problems with the Caravel and fixed them, that would love to chime in and tell you what they did to solve their problems if I would only shut up now. So I will.