This information is empirical.  Real information is available by scrutinzing
the schematics in the nth-generation copy of the service manual...

The following is the Vectrex Cartridge connector pinout.

Pin #     info source    designation
-----     -----------    -----------
1         Ohm            HALT* (MPU 40)
2         Ohm            Vcc (MPU 7)
3         cart           A7 (ROM 1)
4         Ohm            Vcc (MPU 7)
5         cart           A6 (ROM 2)
6         cart           A8 (ROM 23)
7         cart           A5 (ROM 3)
8         cart           A9 (ROM 22)
9         cart           A4 (ROM 4)
10        cart           A11 (ROM 21)
11        cart           A3 (ROM 5)
12        cart           OE*/Vpp (ROM 20) (LS32 1)
13        cart           A2 (ROM 6)
14        cart           A10 (ROM 19)
15        cart           A1 (ROM 7)
16        cart           CE* (ROM 18) A15 (MPU 23) (LS32 2)
17        cart           A0 (ROM 8)
18        cart           D7 (ROM 17)
19        cart           D0 (ROM 9)
20        cart           D6 (ROM 16)
21        cart           D1 (ROM 10)
22        cart           D5 (ROM 15)
23        cart           D2 (ROM 11)
24        cart           D4 (ROM 14)
25        cart           GND
26        cart           D3 (ROM 13)
27        cart           GND
28        cart           GND (ROM 12)
29        Ohm            A12 (MPU 20)
30        Ohm            (PIA 22) (35 Ohms to R/W* (MPU 32))
31        Ohm            A13 (MPU 21)
32        Ohm            (LS32 3)
33        Ohm            A14 (MPU 22)
34        Ohm            NMI* (MPU 2)
35        Ohm            (PIA 16)
36        Ohm            IRQ* (MPU 3)