This is a two-terminal flasher used to flash the indicator lamps in a car.
It will directly replace the older types which use a heat activated bi-metal strip to achieve the on-off "flash"
It uses no moving mechanical parts (transistor switching)
Therefore there is no "clicking" sound as with the traditional type.
I found the circuit on the web, and have prototyped it to verify that it works.
T1 and associated components form a RC oscillator
of about 1.2 Hz or 70 flash's per minute
The 10K resistor and 33uF cap at T1's emitter determine the timing.
TC= 0.33sec (TC= C x R)
Initially T1's emitter is held near collector potential and therefore T1 non-conducting.
When capacitor is charged; T1 turns on, biasses T2/T3 on , lamp glows and RC network discharges through lamp circuit.
T1 turns off, cycle then repeats
T2 & T3 are a darlington pair; used to give enough gain to switch the lamp current of approx' 1 Amp
As this is a polarized device (as compared with the bi-metal flasher which isn't)
a series silicon diode will peclude any circuit function if "reverse connected"
My example works fine....

Original circuit and redraft.

Version 2:
Uses MJ1000 darlington transistor(s) to replace T2, T3
which reduces component count and build size