Weirdly my alt light is on as soon as the battery is connected regardless of whether the ign key is on or not. ( temp + pressure gauge from a six)
I have the thick red cable going to the battery via the starter, The thinner red to D+
the brown wire to D-
the black wire to DF
If I disconnect the D+ the light goes out. D+ and DF both measure 12v. Any idea where i've cocked up?

914 alternator wiring harness to 911 harness

914 .......... 911
RED D+ .......... Pin 11 (Blue)

Brown D- ........... Pin 12 (Brown)

Green DF ............ Pin 13 (Black)

The thin red wire is always hot ... I just wire nutted it off.

Now, I'm going out to my car to verify I wired it as above, but I do know the thin red wire is always hot.

Yep .... that's how I wired mine

Thanks muchly Ron - so my D+ should be the blue wire. Makes sense now (DOH!)