Based on the date of the Electrical Assembly Drawing (which if you look at closely, shows the solenoid mounted on the steering column, but no vacuum motor) that you Posted (September of 1966 ? the second month of 1967 production), IMO, this may have been an original concept for the location of the Solenoid Valve (3DE536) but was never implemented. I say this for several reasons :
1) As far as I can remember/ know, there have been no pictures Posted here of the Solenoid Valve installation being on the Steering Column. That is not to say that there weren?t any, so if anyone has this type of installation, please Post pictures of it.
2) The 1967 Chassis Assembly has two pages that show the both the non-Tilt and Tilt Columns. The first (copy attached) is of such poor quality that one cannot make out the Solenoid Valve. The second page (copy attached) clearly shows the Solenoid attached to under the dash. Unfortunately, neither page is dated.
3) TSB No. 919, Dated October 21, 1966 (copy attached), clearly shows the Solenoid bracket in position to be mounted under the dash, and also grounded to the dash (no wire).
4) The Shop Manual (dated March 1967) and the Vacuum Manual (undated, but after October 1966) both show the Solenoid Valve and bracket in position to be mounted under the dash (copy of each attached).
5) The Service Part Number shown in both the 1967 only, and the 1960-68 MPC?s are both C7ZZ-3D536-A, which includes the mounting bracket. Obviously, the same bracket that would be used to mount the Solenoid to the Steering Column would not be the same as that used to mount it under the dash. While a change in brackets by itself may not warrant a change in suffix (-A to ?B), a change in bracket and its mounting location, might.
In summary, IMO, I believe that if/ until we have evidence to prove otherwise, we can say that the Solenoid Valve was mounted under the dash, to the right of the steering column, and without a separate ground wire.
Bob