Although my 2002 V40 came with factory remote central locking, I decided to fit a cheap universal remote control as the factory key was in a poor state and didn't always work.
It was a bit of an ordeal to fit, mostly because I needed access to the central locking/alarm module (VGLA) and it is located underneath the radio.
So I had to remove the radio and the centre console panels.
The easiest way to wire in the universal module was to connect it up to the signals that connect to the lock switch on the door.
I took power from the central locking/alarm module: you can get constant 12V from either pin A26 or pin B1.
I took ground from pin A1.
Unlock is the grey wire going into pin A4 and lock is a green/yellow wire connected to pin A6. These need to be connected to ground to trigger.
On my universal module, I connected ground to the common (COM) wire for both lock and unlock, and then the car's lock and unlock signals to each of the normally-open (NO) wires.