Most Subaru radios have a standard "Motorola" style antenna connector (big, round coax). On the radio pictured in post #2, the socket is at the far right corner of picture, shown with the antenna cable plugged in.
Models in the last several years that have the antenna wires on the rear glass have an Antenna RF Amplifier
unit (usually hidden in a rear pillar). See the note in the previous section about the Antenna Control Pin on the wiring harness.
Worth noting: On some older Subarus (including all SVXs), the antenna connection is a "pigtail" -- a wire runs into the back of the radio and is soldered to the PC board inside. If you follow the wire about 1-2 feet away from the radio, you'll find the standard Motorola connector there. In the SVX, it's under the carpet on the left side of the transmission hump.
In 2005–up Legacies and Outbacks (not Outback Sport), Subaru changed from the Motorola plug to a smaller, proprietary connector. The other models did not switch. UPDATE:
Some 2008-up Imprezas and 2009-up Foresters now use this connector too.
Rear of 2005 Legacy radio:
(picture posted by jp928 in the thread "cd CHANGER SOCKET ON 05 hu" on LegacyGT.com)
The antenna connector is the gray plastic plug at the lower-left of the picture.
Note that there are two mini coax wires running from the radio to that connector. Has Subaru brought back radios with Diversity (dual antenna inputs)? I haven't found mention of any recent cars having second antennas (not since the SVX).
Close-up of the radio's antenna socket (with Motorola male and female plugs above for size comparison):
Each of the two smaller rectangles inside that shell has two metal contacts -- the center "hole" connects to the coax wire's center conductor, and a metal sleeve on the outside of the rectangle connects to the coax wire's shield.
started producing adapters in late June 2005. Check with your favorite after-market car audio retailer for availability. Part numbers 40-SB10, 40-SB20 (reverse), and 40-SB30 (pair). Here's the page from Metra's 2005 catalog:
The other harness manufacturers also have these now -- Scosche part numbers SUAB and SUARB (reverse), American International part numbers SU-6, SU-7 (reverse), and SU-10 (pair), and Best Kits BAA26, BAA27 (reverse), and BAA2627 (pair).
Each adapter only has one Motorola plug or jack and one coax wire. So if any of the recent Subarus have dual antennas, you'll lose the second antenna by using these.
Some recent Nissans have an antenna plug that looks very similar (with a rectangular, gray plastic connector, with spots for dual antenna cables). However, the adapters for those will not work in Subarus
! Although at first glance they look the same, the Nissan plug is wider and has different keys.
Do not pull the small coax wires. These connectors are somewhat fragile, and many people have accidentally ripped the wires out of the connectors. Only hold the gray plastic shells. The car's antenna plug has a release button on one of the narrow sides.