another electrickery thing

[dobber]

just built a recovery truck based on the ex tesco iveco 3.5 chassis cab, i put smaller led rear lights on the rear which was a simple cut off the plug thing that went in to the original rear lights [ damaged hence the leds] , find the earth and connect up. simples !... NO.
6 wires,

indicator
side
brake
reverse
fog
and earth presumably

every thing connected via a process of elimination and working fine except the fog light, im left with a constant live  both sides which doesn't alter no matter what i do with the fog light switch.  only goes dead when the ignitions off.
thought at first it may be the switch works the earth but without the earth nothing else would work.
am i missing something simple? wired the trike from scratch with guidence but this is baffling me.
any idea from the resident experts

[fifer]

I am no expert , but I thought that the power feed to the fog light switch comes direct from the main light switch when the lighting switch is in the headlamp position { sometimes wired from the sidelight terminal on the main light switch }
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With the fog light wired up try removing one wire from the rear of the fog light switch and see if the lamp goes off .
To eliminate a faulty fog switch { maybe sticking internally } do the following .
With the fog light wired up try removing both wires from the rear of the fog light switch and the lamp should go off .
If the lamp does not go off then it is receiving power from another source .
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If the lamp does go off just touch both wires you removed from the fog switch .
If the lamp goes on when the wires are touched and goes off when the wires are not connected  then the switch is sticking internally .
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Just out of curiosity , what colour is the foglamp wire which is live till the ignition is switched off ?
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Just had a thought that this might be one of those modern lighting stuff with resistors , ecu and lots of multi terminals so that what I have put above does not apply ?
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[dobber]

thanks fifer,, the switch is only live when head lights on as with most motors, we have checked on the other iveco we have and it is the same, a constant live. i need to strip the broken  fitting and see where the wires go and connect i think.    the iveco do have the check light thing that comes up on the dash, hence we had to put a relay thing on when we wired the towbar up or the system gets confused.