Analogue-sequencer

> The 808 however will have to be synced by the Doepfer MCV24 
> instead until I
> can figure out how to cut the pins on the cable properly. 
> It's very strange
> that the MCV24 works without having that 4th pin removed.

The MCV24 is purely a DIN sync output.
The P3's wiring is a combination of both DIN sync - using pins 1, 2 and 3;
and MIDI - using pins 2, 4 and 5.
Pin 2 is ground for both DIN sync and MIDI.
Pin 4 is not normally used by DIN sync, but is used by the 808.
The easiest way to break the pin 4 connection involves a DIN cable, a pair
of pliers, the pin, and metal fatigue.
Bear in mind the cable will be no use for MIDI once you break that pin.
It may be neater to break the pin 4 connection inside the 808.

Best regards,
Colin Fraser
Sequentix Music Systems Ltd
http://www.sequentix.com