New MC and Prop valve equals light issue

[Mickm69]

Hello all,
I have just installed an ECE disc brake conversion on my '69. I had no issues until I plugged the electrical brake wire cap (brown wire) on the new prop valve and now my brake light stays lit.
The brake, turn signal lights all work correctly. If I unplug the brown brake wire the light goes off.
Can anyone shed some light on what my issue could be?
All help will be appreciated.
Cheers!
Mickm