Mondial ignition light

I have a 1982 mondial QV eurospec, this morning the car was working normally but when I turned the engine off and took the key out, the ignition light stayed on, although not as bright as usual. When I turn to ignition on the light goes out! However, the car will then start and run normally and all the other electrics work OK. I have disconnected the ignition switch and bridged it with another switch, which makes no difference. I have also put back an old fuse box, which makes no difference. I have checked all the connecting boxes under the dashboard and all the earthing wires, they all seem OK. So, when the ignition is in the off position the light is on and the electrical circuits are charged i.e. wipers etc. but when the ignition is in the on position there is no light. Any help will be greatly appreciated as I now have to take out the key and disconnect the battery.
Many thanks

 

many thanks, its the rectifier(diode pack) in the alternator! however,there is no number on the bosch case to identify the part and there are over 90 different types! any ideas? thanks again for your help

 

hi,had a problem tracking down the rectifier no. however Bath Auto Electrics(01225 832053) in the UK sent off the part to their supplier who matched it. They have rebuilt the alternator and only charged £100 inc tax which is £150 cheaper than a second hand one from a leading Ferrari "specalist" and £350 cheaper than a new one! Onwards and upwards!!