On Nov 19, 6:17 pm, wrote:
I replaced a regular 2-way indoor switch that switches my outdoor
patio incandescent light on/off with a timer switch.

I followed the instructions and the timer works fine, The problem is
that when the timer switch is in the off position, the patio light
flickers
(with a very low light).

I bought another timer switch of a different brand, and the same
thing happens. Does it mean that all timer switches leak?

Both timer switches have a programmable electronic clock,
and use the same external wiring (black wire, blue wire,
red wire, ground/bare wire).

There is one thing. The regular 2-way switch did not use
the ground wire, it connected only two black wires.
The wiring behind the switch uses two 3-wire cables,
each cable has one black wire, one white wire, and one
bare wire. The white wires and bare wires are tied together,
and only the black wires go through the 2-way switch.
However, I did connect the bare wire from the timer switch
to the bare wires from the cables as the instructions
stated.

Sounds like:
White to white. Not connected to anything else? This is the neutral or
un-switched lead through to the porch light.
Bare wire to bare wire (this is the grounding/safety wire) connected
to the metal box etc. and while there for safely connecting any metal
parts that one could come into contact with, does not under normal no-
fault conditions actually carry any of the electrcity to operate the
light/s.
The black wires 'to' and 'from' the switch. This single switch
controlling the flow of of electrcity through the live (black) lead to
the porch light (or lights?).
Please confirm the above. Have an idea what is happening with an
electronic timer such as this; but do you have a compact fluorescent
bulb in porch light?