Just send the "signal"(yellow) to the tip and ground the red and ground together, that essentially makes it a mono plug(if i remember correct) or use a mono plug for the same results
This will probably *not* work.
If you want to send the same signal to both channels, do this:
red > tip and ring together
yellow + shield > both to sleeve/ground
That will not handle loud volumes. To handle loud volumes you need to insert a 4.7k resistor between the yellow and shield wires.
Now, that said, if you don't understand this, I suggest sending it to someone who does. Chris Church or perhaps Busman. Those guys will sort it out. I don't think you can burn anything out connecting it as above, but it is not likely to work properly either.
Richard