Lighting – Light switch timer for outside lights

From the looks of it, there are only black, white, and ground in the junction box. This most likely means it's set up as a switch, and the white wire is actually a switched hot (and should be marked with tape or marker with a black or red stripe).

Unfortunately, since your timer requires a neutral, this isn't quite going to work.

What you need to do is:

• Open the main panel
• You should find:
  • The black from this junction box goes to the breaker
  • The white is connected to a black wire that goes off to the fixture
  • The white wire that goes off to the fixture is connected to the neutral bus

If this isn't the case: stop. Update the post, as my instructions won't help.

• First, route the wire that goes off to the fixture into this junction box
  • Ideally, you would do this outside of the breaker panel
  • You may need to use wire nuts and run a new wire into the junction box
• Second, run a new wire from the panel to the junction box
  • Connect neutral (white) to the neutral bus in the breaker panel
  • Connect hot (black) to the breaker in question
  • You may be able to use whatever wire is there now for this, impossible to tell without opening the panel

You should now have in the junction box:

• Black + white + ground from the panel (black from the breaker, white from neutral bus)
• Black + white + ground going to the fixture.

Basically, just connect it up exactly as that diagram shows:

• Connect grounds together, and to the fixture
• Connect neutrals together (including the white wire on the timer)
• Connect black from the break to black on the switch
• Connect blue from the switch to black to the fixture

Presumably the black and red wires are the hot and switched, corresponding to your current switch. If the box is gounded, that one's good. The issue (depending how the box is wired) may be that the timer needs a neutral connection, and if the box only has "switch loops" run to it it may not currently HAVE a neutral wire - in which case you need to get one there.

Now, when you say that there are 5 cables in the box, do you mean 5 multi-wire cables (black-white-bare/green) except one of them is red-black-white-bare/green and there are a lot of white wires connected to each other? If so, it's your lucky day, as one of those white wires will provide your neutral connection. Avoid white wires that are connected to switches, as those probably are NOT neutrals.

A picture would help a lot, but that's my educated guess, if you are using "cable" in the usual sense, as opposed to confusing it with "wire."