On my 84 Westy, the rear speaker wires run there encased in a black
plastic sheath.  Perhaps it is the same on your 85.  Not a good 12 volt
source in this case.

I agree with Malcolom, get the 12v from the kitchen light or driver's
light.  That's how I did it when adding interior lights to my Westy.

I hope this has been illuminating.............

Best wishes,

Tony

Anthony L. Mourkas
Hampden, Maine, USA
1984   Vanagon Westfalia    "Gertrude"
1986.5 Quantum Syncro Wagon "Wolfgang"
1991   Jetta Eco Diesel     "Liesel"

>I'm in the process of installing a small interior light above the sliding
>door on my 85 Westy.
>
>Have the Vent channel above the door partially disassembled.
>
>I notice there is a black cable coming from the front.
>
>What is this and if electrical, would it be a goods place to tap for power
>to the light?