Paul,
***Apologies for a long post hopefully a read through might help you to get to the bottom of the flickering light.***
I have redrawn the diagram to help me understand how it all ties together with the wear sensors.
You will see the +12v comes to the bulb, the bulb is then ground by the low fluid switch or a ground from the handbrake switch or one of the wear sensors.
On top of the fluid reservoir you have 3 wires. one goes to ground, one to the bulb and one the the wear sensors/handbrake switch. You should have the ground on its own as this is only for the fluid level switch. The other 2 wires are piggy back connected. So you can isolate the two parts ie. remove the connector for the wear/handbrake would only leave the fluid level switch operating the warning lamp and if you remove the piggybacked connectors from the lid but connected to each other the other part of the system will operate the warning lamp.
Fluid level is simple, the cork float drops and makes a connection illuminating the warning lamp.
Handbrake switch, operate handbrake and the switch grounds completing the loop through the wear sensors to the bulb via the piggy back connector.
Wear sensors, inside each pad there is a wire which loops back to the plug which connects to the loom. when the pad wears the wire gets worn through and when in contact with disc completes the circuit to the lamp via the piggy back connector.
That is how the system basically works. This brings a couple of things to mind. If there is a brake pad missing or not connect then the link to the handbrake switch is missing. Does the handbrake bring the lamp on? I remember that at least one of the pad plugs in the loom had a terminal corroded (not sure if you sorted them) . If the handbrake works the lamp correctly then I suspect there may be a bypass of the wear sensor side.
I would pull the wires off at the fluid cap, drive about if there is no flicker with just the handbrake/wear circuit connected then it is the fluid switch. If it does flicker there could be a chaffed wire. Going by the diagram the handbrake switch is at the end of the line so if you then disconnect the brake pads rear to front and see if there is a flicker or not you will at least have an idea of which section of the wiring to look at. The P6 has a pretty simple loom so shouldn't be to bad.You may also have the old crust snap connector problem, I would think that there is some behind the rear seat as the wires drop under the petrol tank just above the diff.
Colin