<div class="bbWrapper">Here's the deal: original AM radios had a two-pin speaker connector. Original AM radios with fader controls had a 4-pin connector, as did all AM/FM sets. I'm talking 1964-66 cars. I'm not sure if a fader AM set was available in 66, as the AM sets I've seen are all leftover 65 sets, but the fader wiring for the AM/FM sets are different in 64-65 and for 66. Same connectors but wired differently.<br />
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That being said, a rear-speaker car has an additional wiring harness. It has a four pin connector for the radio, a two-pin connector for the front speaker, and three wires headed for the back. One of those is ground, connected to a lug under the glove compartment. the other two go to a rear two pin connector that's similar to the front speaker.<br />
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For what it's worth, my car is in the shop, and the fellow had removed the back seat. While back there I asked about replacing that speaker (nolt original, for a stereo). I gave him a 6x9 to try and see if it fits under the two posts. It DOES! I now have a 6x9 back there; better than the 5x7.</div>