Working out which wires to connect!!

[f1steveuk]

Here's one for the electrically minded. We have a very useful "dusk 'till dawn" lamp at the bottom of our outside steps, which isn't connected!. Having taken the front off, it is wired up, one orange wire, one red wire, one purple wire. Going into the house, and to the fuse box there is a birds nest of unconnected wires, and it would appear the old French owner brought a job lot of, yep, you guessed it, red, orange and purple wire. So I have a lamp, connected at one end, and no way of knowing which of the very many tails at the fusebox are connected to it and to connect to get the thing working. Suggestions please!!

[Chancer]

With the thing disconnected including any lamp powered from it and within daylight hours (not sure if that is necessary without power) use a multimeter set to I dont know, 2K ohm range and measure across the conductors, there will be a resistance across the live and neutral wires, the third wire should show no resistance to the other two, that will be the switched output.

Then you have a 50/50 chance on the polarity of the live and neutral, it will probably only switch when its correctly polarised.

hope that makes some sense.

[f1steveuk]

So, just so I understand, the two wires connected to the lamp will show a resistance, because they form part of a closed circuit, connected to a source of resistance (the bulb), whereas wires not connected at both ends will show nothing? Though that would mean every disconnected wire could be my third wire!!

[powerdesal]

''... there is a birds nest of unconnected wires,...''

Sounds like a total rewire is in order, using proper colour codes.

The alternative is to disconnect at the lamp, attach a trailing lead core to each lamp end wire in turn (chocolate block is ok ) then run the trailing lead to near the fuse box. Using a multi meter, connect one probe to the trailing lead and use the other probe on each of the unconnected wires at the fuse box until you can see continuity. Mark the leads and repeat as necessary to identify each end of the lamp wires.

[Chancer]

[quote user="f1steveuk"]So, just so I understand, the two wires connected to the lamp will show a resistance, because they form part of a closed circuit, connected to a source of resistance (the bulb), whereas wires not connected at both ends will show nothing? Though that would mean every disconnected wire could be my third wire!!

[/quote]

No!

When I speak of wires it can also mean the terminals on your photocell, some have unterminated wires coming out, others have a termimal block.

The two wires (terminals) that form the sensor circuit, the live and neutral will show a resistance (might be higher than whatever I said, cant see it in this window, might be over 2Kohms) the resistance being the electronics, the 3rd wire (terminal) will normally be isolated only when the photocell switches at dusk will it be connected to the live feed to switch the lamp, thus by testing the 3 wires (terminals) the two between which there is a resistance will be the live and neutral and the one that is isolated will be the switched feed to the light bulb, these tests of course must be taken with the unit diconnected from the mains and the light unit.

[Jonzjob]

Nuffin wrong with a nice neat job.

[URL=http://s47.photobucket.com/user/Jonzjob/media/Johns/Jar-a-worms.jpg.html][IMG]http://i47.photobucket.com/albums/f180/Jonzjob/Johns/Jar-a-worms.jpg[/IMG][/URL]

If you check you will probably find several plastic covers around the various walls in the house, about 4" x 6". Above is what you will probably find behind the covers. I took one look at that one and put the lid back on smartish [:-))]

[PaulT]

Yep, rewire

If you have all those cut ends in the board then it sounds an absolute mess. Correct colours and with the correct circuits a far better job.

[Gyn_Paul]

First of all, I would tease the bird's nest apart and see if I could get an idea of which bunches of wires are heading off in which direction, and look for a group of wires in the appropriate colours.

Then I would disconnect the wires from the light, and tab a cable onto each of the wires in turn, running it back to the fuse box. Now you can put a meter across the ends and look for loop continuity.

(if it's too long a run, or too much of a faff, 1st check that none of the bird's nest is earthed, then connect - in turn - the light 's wires to a local earth, then earth one side of your test meter and again look for loop (earth in this case) continuity among the bird's nest.)

I'm assuming in all this, that none of the wires in the lamp has any volts present on them!

[powerdesal]

As I suggested 4 posts ago !!!!! :-)

[f1steveuk]

I have, bit by bit, been tidying up the wires that are near the fusebox, and it has become a little more easy to see, and I can also see  where he was attempting to put in extra lights etc, but as I say, all been pulled through, not connected at either end, and all in red, purple and orange. The only wires connected are the ones at the lamp, but only at the lamp end, so no voltage!!. It's all quite close together so trailing a wire back from each connection is the likely way forward, and then label them all!!

Not having a tester could I (baring in mind none are connected!!!), connect these wires in a circuit with a 12v car battery (which I do have a spare one of) and just use a 12v bulb ?

[Araucaria]

[quote user="f1steveuk"]

Not having a tester could I (baring in mind none are connected!!!), connect these wires in a circuit with a 12v car battery (which I do have a spare one of) and just use a 12v bulb ?

[/quote]

Testers - multimeters - are very cheap, and everyone should have one. That said, what you suggest will certainly work, but please please make sure that you have turned all the 240v electricity off at the meter first.