How can I make a simple circuit to output only after a min input voltage is exceeded?
Here are two circuits which are potentially suitable.
A more complete knowledge of your situation is needed to design with certainty.

The left hand circuit outputs a voltage which is Vzener less than Vin.
C1 acts as a filter capacitor to provide DC when a blinker signal is the trigger.
R1 serves to provide a minimum load to the zener and to dissipate the capacitor energy when the source signal is removed. 

The right hand circuit enables the transistor only when input voltages well in excess of 10V are present. As shown it tracks Vin when it is flashing. This could be changed if needs be. eg a capacitor on Q1_C or at Q1_b could be arranged to assist. 

Q1 base drive voltage = Vin x R2/(R1 + r2) = Vin/28 with the components shown.
For Vin = 10V, Vbase = 10/28  = 0.36V
For Vin = 24V, Vbase = 24/28  = 0.86V.
The transistor needs ABOUT Vbase = 0.6V to operate.  

D2 and C4 form a reservoir to operate the circuit from briefly if the input is pulsing and a steady on trigger voltage is required. If a steady output is not needed then D2 can be shorted and C4 omitted.

R4 discharges C2 when Vin is removed if the output load is not adequate to do so in reasonable time.

The circuits can be 'improved' if more information is provided on the requirement. 







simulate this circuit &ndash; Schematic created using CircuitLab