This sound system is exactly like the one RC4WD sells and they are both knock offs of the Servonaut SMX. One set of paired black and red wires can be used as an input for the speed of the engine sound, instead of using input from the receiver the two wires hook to the motor wires and as the motor speeds up and slows down so does the sound. The other set of paired wires is used for a special horn sound that requires a separate board and speaker. The black and red wires that are separate are the power in for the sound unit.
Connect the SMX to the battery via the red (+)
and the black (-) cable. The yellow cables have
to be soldered to the loudspeaker. Plug ‘FR/ESC’
(blue housing) into matching port of the Servonaut
speed controller (‘Sound’ connector). Starter
and horn (F1+F2) are controlled via another receiver
channel (here: channel 8). Cables F3 and
F4 are normally used in conjunction with a multiswitch
(e. g. Servonaut MM4). F3 switches the
‘Martinshorn’ (a special sort of alarm siren used
in Germany). F4 is used to simulate an auxiliary
drive. You can connect F4 directly to the drive
motor as well. Functions F1+F2 and F3+F4 can
be interchanged (see chapter Switching Functions).
The SM+ add on is installed as shown
(short cable plugged into SMX, long cable
plugged into free receiver channel, here: receiver
channel 9).