Latching Relay
ERROR: 85 & 86 should be reversed

A simple circuit that can be used for a variety of applications. If the diode is replaced with a wire, the circuit will still work, but if the relay contacts ever fail, the ON switch will carry all the current to the load while it's pressed.

The 2 switches can be replaced with a DPDT momentary up-down switch, or existing switches in other circuits could be used.

For example, the ON switch might be the START circuit of the ignition switch; the OFF switch might be the RHR power window switch; and the load might be an auxilliary horn. If the vehicle is ever started without the RHR window switch in the correct position, the auxilliary horn would latch on as a theft alarm until the RHR window switch is pressed. Since window power is disabled during starting, the circuit wouldn't backfeed if the switch is held during cranking.

Owner caption January 2006 · Photo 1185 of 5000