alternator charging lamp dash circuit on 83 300td

I've been repairing burnt tracks on the circuit board behind the instrument guages and in trying to fault find a root cause have come accross a problem with the alternator charging lamp circuit.

The haynes manual shows the alternator dash lam circuit coming in on pin #7 of the 15 pin connector that goes in the back of the panel. I have a blue wire in that pin #7. However, the wiring loom has a blue/brown wire with a bulb socket on the end and this thing was in the socket for the alternator warning lamp. I checked the alternator and it has the same blue/brown wire.

Theproblem is that the bulb socket attached to the wire just lays loose in the hole in the circuit board - ther eis no firm electrical connection - seems that something is missing.

If I simply remove one of the indicator lamps from the dashboard and plug that into the alternator warning lamp socket, then the light comes on when I key on {engine does not run so I can't tell if it goes out ot not when I start}

So problem is :
1. I have a mystery 'blue' wire attached to my pin#7
2. I have a blue/brown wire that comes from alternator to a bulb socket that can't seat positively in the instrument panel.

The haynes manual refers to a blue/brown wire but going to pin#7.

Confused.
Steve