Review on 📈 ELING 85mm Tachometer RPM Tacho Gauge with Hour Meter for Car, Truck, Boat, Yacht - 0-6000RPM with Backlight by Corey Evans

I bought 2 cars to replace the flybridge. I have two internal 454 Crusader boards powered by the coil. The instructions list a tachometer sensor and an alternator. There is no information other than the speed ratio. 8-cylinder shows to set it to 4.0. Everything is fine, but nothing is readable. I took my professional tachometer and tested the output signal wire on the dash and it works great. So the Eling-Touch does not read the signal. So now I have two useless cars. IF ANYONE HAS INFORMATION HOW THEY MAY WORK, I'M ALL EARS!. I was a certified marine mechanic and I'm at a loss. Someone misplaced a ground connection? It does not make sense. I don't want to short out my other touch on the station's main panel.