towbar wiring problem

[pv544t5]

Hi.
Although its nothing to do with "performance",Can anyone help.fitted a genuine volvo trailer wiring loom today.plugged in my trailer board to test it.lights-ok,indicators-ok,but when i put my foot on the brakes,The lights initially lit then stopped working,including the cars brake lights !!.checked the fuses-all ok.disconnected the new volvo trailer wiring loom to try and eliminate a problem there,tried a spare bulb failure unit,checked continuity of brake light switch( was ok but suprised that it seemed to be a normally closed contact? open when brake applied?).still no brake lights.been following brake wiring diagram in haynes manual.anyone with any ideas? .95 volvo 850 t5r estate.
Pete

[t5 stealth]

at a guess id re check the stop light switch on the pedal,
if you bridge the terminals on it the brake lights should work,
if it does then the switch is nackerd,

and make sure the earth is a good one.........towbars are usually white wire is earth...
not sure about factory one tho.