I don't use the metra, so I don't know the wire diagram. Your problems sounds like the relay is staying latched. It could either be a poor relay or your source switching the relay. most likely it has to do with your source. If you have a wire diagram could you email it to me or post it on here.
Mikegett@msn.com is my home account. I have high speed so don't worry about size. Have you ever opened the metra up? Is there a cicuit board containing the relays or is simply a box of relays? Due to its simplicity, I would think the later would apply.
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2003 Maroon Alero GLS Sedan. (Purchased new in 2003 with 18 miles, and sold in 2006)
2004 Toyota Corolla LE (Purchased new in 2003 with 87 original miles)
2007 Toyota Camry LE (12 original miles)