That’s the first thing that crossed my mind when you made me aware that it worked fine with 4 pin bikes but not with your 6 pin. It tells me the tuner was designed for 4 pin, so I still suspect it’s the cable. If you can find one more bike with a 6 pin connector, I think you can answer that question. Other than de-pinning the connector so that the correct wires from the 6 pin align with the corresponding wires of the 4 pin it’s not going to work, and you’ll probably fry something in the process, so don’t do that. It’s unmarried so you could sell it to someone who’s bike it will fit, and get another reputable tuner like a TTS, Thundermax, PowerVision, an 08C, or even an FP3 if you’re going to keep things simple.