The AUX connector on the back of the radio is numbered like this:
 -------------------
 < 3  6  9  12  15 |
 | 2  5  8  11  14 |
 < 1  4  7  10  13 |
 ---^----------^----

The pinouts are as follows:


1) Hookswitch - 5V offhook, 0V onhook
2) ME (Mic Ground)
3) IGN (Ignition Input) (can be used in conjunction with clipping W101)
4) DEO (Discriminator Output)
5) MIC (Mic High)
6) ES1 (External Speaker Output)
7) SB Source Voltage (13.6 while radio is ON)
8) PTT (Active Low)
9) RS2 (Output for INTERNAL Speaker) (should be tied to pin 12 for audio on front speaker)
10) HN1 (Horn output if applicable)
11) HN1 (Horn output if applicable)
12) ES2 (External Speaker Output)
13) OS1 (PA speaker Output)
14) OS1 (PA speaker Output)
15) Ground