Graeme
Do you mean the diode board inside the front cover ?
That is the main diode board which converts the AC output from the 3 phase alternator to DC for battery charging.
It has a number of large and small diodes and there is no reason why they can't be individually replaced if you know that one of them is faulty. The large ones in particular would need to be carefully soldered as they are passing a substantial current.
However your original neutral light problem is nothing to do with this diode board.
Bob has given you the possible locations of the single diode which can cause your problem depending on the year of your bike. If it's an LS
I think the diode is in your starter relay.
