The Problem

Older vehicles often lack the wiring infrastructure to support modern reverse lights or backup cameras. Rather than doing a full wiring overhaul, I designed a small sensor module that detects when the transmission is shifted into reverse and automatically triggers the reverse lamps—no factory wiring required.

How It Works

The sensor monitors the transmission output using a hall-effect sensor to detect rotational direction. When reverse rotation is detected, it sends a signal to a relay that switches the reverse lights on. The whole circuit is self-contained, runs off the vehicle's 12V system, and is fused for protection.

Build & Installation

The circuit was prototyped on a breadboard, then soldered onto a compact perfboard and heat-shrink wrapped for weatherproofing. Installation took about two hours—tucked behind the dash with a single tap into the fuse box for power.

Next Steps

A future revision may include a small PCB to replace the perfboard, and I'd like to add a backup camera trigger output so the same sensor can wake a rear-view display simultaneously.