Well, by the sound of it, nothing. :?
Just to confirm, to install the pickup (it's 2-conductor, right?) you should have had to do 4 things:
1. Un-solder the old pickup's hot wire from the left-hand tag of the bridge pickup volume pot.
2. Un-solder the ground connection from the back of the same pot.
3. Solder the braided part of the BKP's cable to the back of the pot.
4. Solder the BKP's hot wire to the pot's left hand tag.
If you disconnected or connected anything else, then something's wrong.