any electricians available to shine some light on this for me?

[YoungOffroader]

I was wondering if any of you wise electricians could help me with a wiring diagram to show me how to make a test box i have in my head. at the moment when im repairing wiring to trailers from holand with many "dead shorts" in there wiring everytime i cut one out i put another fuse in and watch it blow telling me to continue looking for another short.
But in me head im sure i can put a bulb in the circuit so that when there is a short it lights the bulb due to it getting a circuit through the short. but the only way i can do it means the bulb doesn't go out when the short is found is just goes dim due to getting 12V and the trailer lights being dim with 12V.
Is there a way of wiring the bulb in parallel at all so it goes out when the circuit is working?
Many thanks for your help

[BigBobE]

so what do you want to do, have a socket on your box, and this socket then has a power supply to it, and a bulb that goes out / comes on when you have a short...

or how do you test each circuit??

[YoungOffroader]

so what do you want to do, have a socket on your box, and this socket then has a power supply to it, and a bulb that goes out / comes on when you have a short...

or how do you test each circuit??

at the moment this box has 6 switches with 6 fuses, one per circuit on the trailer, it plugs into the trailer and if all 6 switches are on and the trailer is good all the lights on the trailer light up, but often there is a short on the side markers so then you would just have the side markers switch on the box and keep replacing fuses all the time. but i would like a bulb to light when the is a short and go out when there is no short but still light the trailer lights.

[YoungOffroader]

i think its also could "overcurrent detection" but im not sure

[BigBobE]

i get you now,

so what you want to do is place a lamp in directly after the fuse,

so that when you have a short you can see a light on, would you go for a buzzer set up??

[YoungOffroader]

i get you now,

so what you want to do is place a lamp in directly after the fuse,

so that when you have a short you can see a light on, would you go for a buzzer set up??

no just a light i think because if it take half an hour to fix then i will be listening to a buzzer for half an hour

ive seen it done but its in another companies service van and they wouldn't let me see how it was done

[YoungOffroader]

im guessing its something like putting a resistor in front of the bulb ao once the short is removed and the current drops bulb goes out but then i get lost

[blackpoolsparks]

This test box you refer to, where does it draw it's power from to light the lamps that tell you all is OK

[YoungOffroader]

This test box you refer to, where does it draw it's power from to light the lamps that tell you all is OK

the 24V power of the van, its wired directly in and the box is mounted on the wall and has 5 meters of 7-core cable with a 24N socket on the end that plugs into the trailer

[blackpoolsparks]

Without seeing it it's difficult to draw you a diagram.
But think about it this way and you should be able to figure something out.

The box probably supplies power to the circuit that it's testing and if that circuit is complete, it lights the test lamp.

When you have a circuit that is open it won't.

Now if you have a short, which is part of the circuit which is in contact with the chassis, or rather any part that's connected to the chassis it blows the fuse

Therefore the chassis forms part of the circuit .

Get it?

[YoungOffroader]

Without seeing it it's difficult to draw you a diagram.
But think about it this way and you should be able to figure something out.

The box probably supplies power to the circuit that it's testing and if that circuit is complete, it lights the test lamp.

When you have a circuit that is open it won't.

Now if you have a short, which is part of the circuit which is in contact with the chassis, or rather any part that's connected to the chassis it blows the fuse

Therefore the chassis forms part of the circuit .

Get it?

not quite it sounds like what ive got. but the circuit is never open as if all the trailer lights are working the circuit is closed through the trailer lights back to earth

[blackpoolsparks]

not quite it sounds like what ive got. but the circuit is never open as if all the trailer lights are working the circuit is closed through the trailer lights back to earth

Yea, that's why it blows the fuse, because it's drawing too much current

[blackpoolsparks]

Hang on I'll try to explain it better

[YoungOffroader]

Yea, that's why it blows the fuse, because it's drawing too much current

yer so what i want now is a light bulb that lights when too much current is drawn but doesnt light when the rite amount is drawn, yet leaving enough current for the trailers lights to light. i think there box had relays in it.

[blackpoolsparks]

Power source = 24 volts and neutral/ earthed to chassis
Put that to lamp = lamp lights up
If the cable is frayed/ cut before it reaches the lamp and it comes in contact with the earth/ chassis it blows the fuse as it's a short circuit

If you disconnect the neutral / earth feed from the van, then the fuse would never blow.

If you then tested the neutral from that circuit to the disconnected neutral of the van, you would get voltage across the cables as you would be completing the circuit with your tester.

This dosent take into account any other circuits or the way the box is wired and is based on testing a stand alone circuit only.

But based on that you should be able to reconfigure your test box