pioneer gm 3400 remote lead

He is asking about the small 3 wire plug that if I remember right has a red, blue and possiby a yellow  wire.  Some of their older decks and EQs got power from the amplifier.  They quit putting the din plugs on the amps, but still put the switched and constant input to power the decks and EQs.  All 3 of the wires require positive voltage.  There is no ground wire on that little plug.  I have seen many of the amps that they lost the plugs, simply soldering a singe wire across all 3 terminals will make the amp come on.

Thank you very much. The amp powers up now.

The only problem is the sub that is attached to it seems to be very quiet, I am using some VERY cheap speaker wire (5p per meter stuff). Would a thicker speaker cable make it louder?

Is the wire thread size?  How long of a run is it between the amp and speaker?  I would use nothing smaller than 18 Ga. wire.  I do not remember that particular amp, is there a knob labeled Input Sensitivity?  Have you tried turning that adjustment in the clockwise direction?