who knows about regulator/rectifiers

[andy352299]

first off i know roughly what the unit does.
i am having difficulty finding a direct replacement for my unit, so i am looking for one from a different model.

my bike gilera 125 apache 1992
the reg/rec is made by motoplat
it has 4 spade connectors
it has 2 yellow wires from the stator - i think this means it is single phase
1 red wire - this has a "switch" symbol on the unit and connects to lights etc
1 red/black wire - this connects to battery, cdi and ignition switch

i have tested it with an ohmeter and i am getting short circuits where i should not.
the bike will ride all day and start with the electric start all the time. but if i use the lights at all they fade to nothing within 5 minutes but the bike still runs the same
the stator appears to test fine.

i have seen plenty of single phase rec/regs for scooters on ebay.co.uk
most have 5 terminals but the fifth one is an earth

apart from the mounting holes being different i do not know what i need to take into consideration.
all advice greatly appreciated