Bob,
isn't the clonker/clacker just a solenoid connected in series between the flasher relay and the bulbs?
Since the current which needs to pass through the solenoid would be lower for a 12 volt setup, maybe you could have left it in place...

Next idiot question.
The standard 12v 2cv battery I have won't go in the 'ole' the 6v one came out of. It slightly overhangs the (presumably) 6v battery tray which is not really a prob. (6v battery doesn't fill the tray lengthways, it's square) but the toasty feet/demister heater air valve is in the way.
So, is there a work round that don't involve me butchering the shell? Is there a smaller 12v bat. that is suitable?
What do you think of using a Mehari type battery 'table' on the r/h chassis leg?
Thanks all.

You can use a smaller 12 volt battery with less amps and less will be needed.

One of the advantages of going 12 volt on the traction is the battery is smaller so you then don't have to take off the whole bonnet to get the battery out, it just slips out sideways.

Yup that was an idiot qustion when I took the big oil soacked carpet underlay heater duct thinghy off the battery slipped in with just a smidge of bending to the vent valve...
Sorry!

A 'happy' couple (or so) of hours have now been spent groping through the Electric Forrest and I've finally (I hope) ended up with Bobh's solution - 12v flasher relay, changed the bulbs & starter motor, headlamp bulb in series with wiper motor and left the rest.
Ians 12-6v gizmo was great, except I rushed off blindly & bought the same one; 5amp. Sadly, even I should have been able to work out that the wiper motor would pull more than that?! The unit seems to have survived trying to run the wipers...
The indicator clacker seems to be working fine on 12v, interestingly the indicators (single 6v incandescent & 2 Led bulbs per side) worked fine on the 12v relay but with the incandescent changed to 12v they went off 19 to the doz. Here I fall down the mineshaft of physics, the 6v bulb must be producing a similar resistance to 2 x 12v, right? It hasn't blown or appeared to burn any brighter than before... But why?

Groan. Everything together, started up Alternator giving 14.3v @ fast tickover rising to about 17.5v @ higher revs not so good, did I wire the regulator correctly...? Never mind that where's all this smoke coming from? Oh yes I remember why this engine was under the bench... All that smoke.
Bugger.
Oh well, plan B. Looks @ 1/2 built M28 on bench. Sigh. Now, if I turn the cross box round, cut off the inlet pipes, swop them over & turn them through 180, then I've got a r/h swan neck exit which wont foul the mastercylinder/clutch frame... I hope.
This is wot comes of hording all that old crap & trying to use it....

crap - was the unit not up to the wiper motor ?

Well it was my bad, 5amp is lighting & such I think, I should have got one that matched the alternator output of around 30amp as I guess that is more in line with 'heavy duty' stuff like the wiper motor - the starting torque on the wipers must be quite high, gearing, resistance of dry blades on dry glass, etc. so the initial current drain would probably be way above normal running draw.
The headlight bulb in line seems to work though... Again my ignorance of electricity, I started with a 12v 65w halogen and it ran about the same speed as it did on 6v, so I thought 'Ooo I'll bung a 12v 40w one on, and, with the bulb pulling less current it will go faster!' Naw. Just about moved and then stalled - wtf? I now know everything I thought I knew I didn't. Why I've never fried myself playing with electricity I can't explain Perhaps someone who knows could explain using very little words? Preferably, if using maths, maths without any letters in, Thank you

Not about me not frying myself obviously, about the running faster with higher resistance, thank you.

6 volt led bulbs have build in resistors so they will bring down the current. 12v leds too but they have other resistors.
We had an argument in the dutch 2cv club. A man told that he had half power headlamps put in serie with another headlamp bulb. He said that the power uses wass less than 1 bulb.... Strange story they ended up in making an testbench and measured that the 2 bulbs used only slighty more power than 1 bulb and not the added up power off 2 bulbs....strange no?