009 Bachmann Baldwin stayalive fitting

[Robertm3110]

I am fitting a Lais872007 stayalive in the Bachmann Baldwin 10-12-D loco.   The loco has factory fitted chip and sound.  The speaker is in the loco coal bunker with 4 wires running to a PCB there.   Two brown wires for the speaker itself and two others, one blue, one yellow to solder points marked L+ and L-   Unlike usual DCC convention the blue wire is the negative.   Can somebody confirm how the stayalive wires in to this arrangement.  I cant see any free solder points on the DCC chip.   Comments appreciated.   Thanks