We found this circuit in an old Mullard (Philips) documentation on the 555 and 556 integrated circuit (double 555). The relay must be 12 V with contacts that support the horn current.
We find this circuit in a technical documentation of 1976. The transistors can be the BD135 and...
12 V battery chargers provide higher unregulated voltage. With the regulator shown, obtained from...
This circuit was obtained from an English magazine from 1980, but as it uses components that can...