broken wiring loom?

[Buckle]

Hello, I would be grateful for some advice.

For the record, I've a 1998 2.5 TDI V6 A4 with 200k on the clock. Despite the mileage, the car drives and looks like new.

Recently the car developed a fault which I need help solving.

In a nut shell, the rear left tail light has lost power. Initially I thought it was the bulb, or a fuse as the onboard dash information system said a bulb had blown. Upon changing various bulbs, and checking the connections and fuses, I've realised power to the tail light has been lost (power is still to the indicator, brake light etc but not the tail light) as proved by a test bulb. As the fault is intermittent, lots of warning beebs occur which is driving me crazy as it sounds on and off driving over bumps in the road.

I've traced the loom from the fuse box under the steering wheel directly back to the rear tail light. As a temporary fix, I've bypassed the broken wire/loom with a seperate wire to the tail light from the fuse box, however my dash still thinks the bulb has blown and gives a warning bulb blown signal and beeb. I think the break iin the connection s somewhere between the fusebox, light stalk and battery.

Can anyone please tell me, wheather, this is a dash fault, a light stalk fault or a computer fault. Perhaps a doggy connection somewhere. Any ideas would be most welcome.

buckle

[Huweth]

Where is the Earth connection? If it goes on and off while going over bumps it could be the Earth attachment. The fault may still be showing on the computer if the bypass wire has a different resistance to what it should be. Electricals are such a pain!

[Buckle]

I know the tail light is earthed as the indicator and break lights still operate.

Does anybody know what part of the car measures the resistance and where it is positioned.

I've tried following the tail light colour coded wire from the fuse box up under my dash but there any hundreds of wires and I get lost as access is rather poor. Any ideas. I expect the broken connection is at the connection wire the wire connects to the computer/part which measures electrical resistance.

?????