Canon N3 adapter for serial shutter control cable

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Hi, I have bought a serial shutter control cable from Astronomiser. However, as my camera is a Canon 20d it needs a N3 connector to connect to the bulb socket. I have this but no way to connect it to the Astronomiser cable. I have a simple Hahnel remote control. If I understand correctly I just need to take off the male end ot my Hahnel cable with the N3 connection at the other end and fit a female connection to fit the connection at the end of the astronomiser cable in to. This is the connection that would fit into e.g. a Canon 300D, which I think is a 2.5mm stereo plug? So presumably I need to connect a 2.5mm stereo socket to do this?

Can anyone explain in simple terms how to do this, as I know nothing about wiring, electricity etc? I now have a few different connections, so must be able to get everything to work! I just assumed the connections would somehow slot together, but they don't! I could buy an adapter from Astronomiser but would prefer to give it a try myself first. I have looked at various internet sites bit find the wiring and connections confusing. I now this should be very simple to do!

Thanks in advance for any advice.

David