Once I completed a radiator (and radiator hose) replacement for my 2004 Mazda RX-8, I moved on to another item that has been sitting on the to-do list for many years. At one point I was excited to add a dashcam to my car, and thought I could do a clean job of integrating one because a wiring harness already exists high and center on my windshield for my fancy rearview mirror. At night it automatically dims in response to bright lights behind me, and it has a HomeLink remote control with three function buttons. (One of which is worn out because I use it for my garage opener.) I saw the same mirror installed across the Mazda lineup so it is not a RX-8 exclusive feature.

Many years ago I visited a RX-8 at a local salvage yard for an unrelated project and picked up an extra fancy mirror along with a segment of its wiring harness. I figured it would help me experiment with how to tap power from its counterpart in my car. It sat until today, when online resources included Mazda wiring diagrams for reference. I didn’t have to determine the pinout experimentally, I could just look it up.

Only four wires were used in this 10-position connector. All four had black insulation, but three of them had a thin color stripe for identification. The Mazda diagram labeled the wire positions A (upper right in picture above), B (lower right), through J. The four wires were:

Position B has a black wire with no color stripe. This wire provides +12V power only when ignition is in the “On” position. This ensures auto-dimming feature doesn’t waste energy when the car is parked.

Position D has a black wire with green stripe. This wire provides +12V power only when reverse gear is engaged. I’m not sure why this is here. Perhaps auto-dimming is disabled when I’m backing up? I never noticed one way or another.

Position F has a black wire with yellow stripe. This is the ground wire.

Position J has a black wire with red stripe. This wire always has +12V power for the HomeLink transmitter.

Whenever I get around to the dashcam installation, I would first try using the black (ignition on) wire for power. Unless the camera storage may get corrupted by abrupt shutdown. In that case, I will use black/red (always on) for power and use black (ignition on) wire as inverted signal to finish writing to storage and perform a proper shutdown. But honestly I don’t think it’s going to happen.