No charge/No charge light with known good alternator

[van31]

Hi all, I just posted on r3v but I'm desperate so here goes.
Alternator/Charging/exciter wire issues
Driving around the other week my car was misfiring above 3.5k and simply mucking about.

After the car dying, I replaced the battery. I thought I was good, and didnt even think to check the idiot light on the dash.
However next time the car died I knew it was to do with the charging system and not to do with the battery itself. Dim lights, misfiring, all that.

I was sent two replacement alternators from my stash at my family's house. Fitted both and the charging light still wouldnt come on. I pulled the dash and there is no power at the light socket. the bulb was fine. There is also no power on the small blue wire (the exciter wire?!) But there is 12v on the red terminal hooked up to the battery.
Is it possible a connection in the dash has died?
I've got to drive the car home and back next week which is a 12 hour return drive, so I want to get this sorted this weekend if possible.

My solution is currently sitting at runing a wire from the battery with a resistor to the exciter terminal, just to get me around.
Does anyone have any ideas? I know the alternator/voltage regulator work because they came off a running car which charged/ran/did everything well. Get a replacement dash? I'm flat out with work and trying to get this done before Sunday/Monday, so any help would be absolutely the best.
Pic is the car a while back. Car is an '85 323i so before the dash was updated with the parallel resistor

[van31]

I've looked at the Haynes wiring diagrams, but the electrical troubleshooting guide seemed clearer.
Page 31 has the wiring diagram which may help.

http://wedophones.com/Manuals/BMW/1985% ... Manual.pdf

[Brianmoooore]

The missing supply to the battery warning light comes into the instrument cluster via a plain green wire on pin 14 of the blue socket, so check if there is power in the plug here first with the ignition on. If not, this wire comes from a splice in the loom in the area behind/below the cluster. Follow the thick green wire from the plug/socket from the ignition switch, and you'll only have to dig a few inches into the loom.
Power must be getting to this splice from the ignition switch, and out of it, on other wires, or the engine, and other things wouldn't work.