2000 Citroen Saxo Starter Motor

Hi guys, got a problem with the wife's car. As far as I am led to believe, the starter packed in last week (just getting a clicking noise). I got another one from a local breakers (he showed me it working on a live engine then took off for me) and when I fitted it on ours, as soon as I reconnect the batter terminals, it seems to be attempting to start itself (motor spinning). There is only 3 connections on it, 1 (on an 8mm bolt) which I presume is the ignition wire, top nut which seems to be for the earth wire as is only long enough to reach the top connection and that leaves the battery power cable which only has to be on the bottom connection. I cant find out if that is right but I assume so (someone else took the original starter off) so I am lost. Changed the 2 wires round and no performance from the starter at all but got me stumped. Ironicallly no local shops have a haynes manual in stock. Can you help asap? The car running is a priority.

Many thanks, SB