The matrix in Table 1 (click to enlarge) contains all possible connections for SMR configuration. Across the top are the 15 standard VGA conductors with their color codes. (Conductor 15 is always used for speaker audio.)
The radio’s control and mic inputs (or outputs at the remote end) are listed on the left. Control inputs (circled) are 1 though 8, and mic inputs are 9 through 16 (also circled). In the first column, on the far left, the ground bridge for each input is listed. For example, if the control input pin 3 is to be grounded, a jumper is placed across Rows a and b at Column 5.
Each VGA conductor (except number 14) can be bridged to any of 4 input conductors. Or, conversely and in general, each input conductor can be connected to one of 4 VGA conductors plus ground. To prevent ground loops, radio grounds should always be connected to the common SMR ground and not to a separate VGA conductor.
A schematic of the SMR circuit board is probably not as useful as a view of the board itself (Figure 2, click to enlarge). It is offered for those interested in experimenting with jumper configurations or tracing the connections shown in Table 1.