Secret Diagram

The circuit can be operated from 4.5V to 12V DC or direct from the brake point of the motor-bike, Resistor R7 should be replaced with 1-ohm. 1/2W in case of an 8-ohm speaker. T5 is a driver transistor. C3 polarity can be reversed for a sudden off of the circuit.

Simple Motor Bike Brake Horn Circuit Diagram

 

PARTS LIST
Resistors (all ¼-watt, ~+mn~ 5% Carbon)
R1, R7 = 2.2 KΩ
R2, R4 = 820 Ω
R3, R5 = 470 Ω
R6 = 4.7 KΩ
R8 = 10 KΩ
R9 = 4.7 Ω, 0.5W

Capacitors
C1 = 22 µF/25v
C2 = 4.7 µF/63V
C3 = 100v/16V
C4 = 0.047 µF
C5 = 0.01 µF

Semiconductors
T1 – T4 = BC148B
T5 = SL100
Miscellaneous
LS1 = 4Ω speaker