The 12s socket usually has 3 lives. One is permanent, the other two are activated via a relay when the engine is started.
So, you need to get the correct one... Normally, pin 4 (bottom or 6 o'clock) is the permanent live via a fuse and pin 3 or pin 7 are both earthed. So If you just need to unlock the doors, stick a live wire in pin 3 and an earth in the centre pin. Job done so long as you actually have a 12s (white) caravan socket
So, you need to get the correct one... Normally, pin 4 (bottom or 6 o'clock) is the permanent live via a fuse and pin 3 or pin 7 are both earthed. So If you just need to unlock the doors, stick a live wire in pin 3 and an earth in the centre pin. Job done so long as you actually have a 12s (white) caravan socket