From Matt's Dad:

I have been involved with helping some members resolve electrical problems so I have put together three documents which may be of help to anyone trying to figure out simple problems with car electrics.
A Simple Guide to Car Electrics
Dynamo Ignition Light problems
Alternator Ignition Light problems
The Car Electrics and Fault Finding Simplified is a generic document and was put together to help teach my son Matthew about car electrics with the aim of showing him around my MGB so is not Fiat 500 specific.

The one caveat is that I don't own a Fiat 500 (Matthew has one) therefore I can't easily confirm the readings on a Fiat 500 electrics and therefore have used readings taken from my MGB and other cars I have previously owned so please use the figures as a general guide. Not being a 500 owner (I prefer cars with the right number of cyliders i.e. 4, one that doesn't have a potential firebomb situated 6" in front of you and one that has brakes with more grip than a block of ice on a teflon coated ski slope) I am not a frequent visitor so can't respond quickly to queries.
I'm only jealous because Matthew gets more attention in his 500 than I've ever got in the "B".
Hope you find them useful. Any suggestions for improvement etc appreciated.
Richard

Many thanks for your efforts. I'll take a read.

Oopsadaisy,

Looks like I am on the right track , looking at the maninuala your dad has written but can you direct me to any posts / solutions to help solveo overcharging on my 500D that insitsts on overcharging ( 16v plus) despite new regulator box?