Charging lamp circuit and function??

[scampbel98]

While I have a degree in electronics, the wiring diagram for the charge light makes no sense to me.
what is the diode bridge function? Near as I can tell, it must enable a complete circuit if there is an imbalance in that bridge, hence some sort of voltage differential which in turn allows the lamp to light if the voltage output is under a particular value??

Ive noticed mine occasionally lights up at very low revs

[baltobernie]

http://www.fiatspider.com/f08/viewtopic.php?f=6&t=14694

[vandor]

I believe the diode bridge is there to make DC current from the AC current the alternator makes.

When the alternator is stopped the wire for the light is a path to ground in the alternator. Since the other side of the bulb gets +12V, it lights up.
When the alternator starts spinning it uses this current as 'exciter voltage' to get the alternator to start charging.
Once the alternator is charging the wire to the light will have charging voltage, so it goes out, as it has + voltage on both pins.

[scampbel98]

Thanks Csaba...
That makes sense in looking at it now.. but what a weird circuit to show you your alternator isn't charging...