From a totaled 2008 Forester I picked up a C123 HU for my 2005 Forester. I got the AUX pod and I removed the interconnect harness for the AUX pod so I didn't have to order one. I had to cut three wires to get the inter connect harness out of the 2008. Two of the wires were coming off the connector at the HU. I'm thinking those were for the sub-woofer based on diagrams in this thread. They are pins 4 and 8 on the connector into the HU.
The other wire I cut came off the AUX pod and going into the 2008 harness.
I put the HU in my 05 and it works but the AUX pod doesn't. When I press the CD button all I get is the CD function. I'm thinking the wire that I cut coming off the AUX pod might need to go to chassis ground to complete the enable circuit. Wondering if anyone has the AUX pod pin out diagram to confirm? Post #324 in the following thread seems to confirm I need to connect a lead to chassis ground.