ive got an annoying problem with my n reg transit van where i have to keep disconnecting the battery overnight so it wont drain the alternator was replaced and is working fine.
It is fitted with a full alarm setup by a company called simba (cant really find much info about them) could this be a posible source of the drain?

 

Aftermarket alarms are notorious for causing battery drains. I'm presuming you have done simple checks like making sure things like interior lights/glovebox light etc are all going out.

If you disconnect the positive lead off the battery then connect a multimeter (set to amps) between the positive terminal on the battery and the wiring clamp you should be getting a high reading. Start pulling each fuse in turn until you see the reading drop. This should pinpoint which circuit is giving you the drain, so you can go from there.

 

i'll give that a go thanks

 

Your first post is a bit confusing, even if the alternator is working fine it can still be causing a continual drain, so might be worth disconnecting this one night as well.
tabetha