Hi SCaro,
Does the installation use an RMI (moving fluxgate driven compass card) ? If so, you may need to isolate compass errors from ADF errors. Position lights are more likely to affect a fluxgate unit and cause the card to move. However, it shouldn't cause the ADF needle itself to move (relative to the aircraft), unless there are "pulsing" things on that circuit, like strobes (which might emit RF that can be picked-up by the ADF receiver). Not sure why the panel lights should affect it, but certain dimmer units can cause problems.
If you turn-up the ident volume on the ADF receiver, do you get any audible noise in the headset/speaker when you turn on those systems you mentioned ?
You've probably already checked, but if you're outside the useable range of the beacon, the receiver will be much more prone to on-board interference, so it's worth double-checking the published range of the beacon you're flight testing against.
If it really is a serious on-board interference issue, then there is no simple adjustment or fix - it's engineer time (maybe that's you). Worth checking the installation's earthing for a start, to ensure nothing has come loose.
B.