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

[YoungOffroader]

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

i think i understand what your saying now thanks alot for that i shall try it during the week

[blackpoolsparks]

Option 2

Use a test lamp to check continuity between the chassis/ earth and the damaged circuit cable

It'll save you blowing fuses

But you probably already knew that

[meooo]

My boss used to replace the fuse with an 8mm bolt and watch for the smoke, then pull the power and fix the cable

[Apache]

I continue to be terrified at the sort of minds that can get trailer wiring wrong again and again and again.

For fecks sake, its not rocket science!

[YoungOffroader]

I continue to be terrified at the sort of minds that can get trailer wiring wrong again and again and again.

For fecks sake, its not rocket science!

its not getting it wrong its time saving, if you put a bulb in the feed it saves blowing a fuse and when the markers light up only half way down the trailer you know where the fault is

[YoungOffroader]

My boss used to replace the fuse with an 8mm bolt and watch for the smoke, then pull the power and fix the cable

sometimes you don't need to when the driver comes in with a 30amp fuse in the unit