I recently picked up a Summit digital air/fuel mixture gauge which has 3 wires coming out the back. Hot, negative, and one to hook up to the o2 sensor. Is there a wire under the dash that I can run it to? Something makes me wanna say its a purple/violet wire?

P.S. Its an 87 T/A with 305 carb. I think I found a couple threads where they talk about plugging into the wire D7 on the 32 pin connector for the ECM. Can anyone confirm this?

Thanks