If the old DIN plug end has even a couple of inches of cable still attached to it, strip the sheath of the cable up to the DIN plug so as to expose the wires. Then using a DMM (Digital Multimeter - Ohmmeter function These are available at hardware stores for about $10), strip about a 1/2" of the insulation off each wire, one at a time and try to locate it by connecting one end of the Ohmmeter to the exposed wire and then searching for which DIN connector pin it is attached to by touching each pin in turn in the DIN connector until the Ohmmeter registers a reading.
Make a drawing of the DIN connector, numbering the pins so that you can write down the colour of the wire next to the pin number (and its location) in the plug.
Do this for each wire until you have identified them all.
Be careful when you touch the DIN pin with the Ohmmeter test probe as you do not wish to 'bridge' the probe between two pins.
Use this image as a guide to numbering your plug. There are a few different numbering schemes, for you it is not important as long as you reconnect the wire back onto the same pin location that you identified when using the Ohmmeter Click on the image to enlarge it for better viewing.