These guys https://www.gravitech.us/stja3brbo.html sure don't tell you enough info. There is a "Jack presence" ; who knows what that means. A contact to ground when the pug is inserted or vice versa?
But it gives you an idea. An external relay could be used to switch in the aux input.
A mount like that would be ok or even just long wires coming out of the unit to a jack plug.
I first need to find out how to tap into the left and right audio feed from the cd player and if it's useable as an aux.
In post number 4 here (http://www.vectra-sport.com/threads/cd30-aux-mod.97399/) Andre mentions this mod and makes it sound easy, but I haven't been able to get registered on that site as they haven't sent a confirmation email.
I'm struggling to find schematics for the cd30 without paying or doing a stupid survey.