I'm installing a Viper 791XV alarm/remote start in my mustang gt and i can't seem to get a good tach signal. I had an audio vox remote start and i had the tach wired to the negative side of one of the injector coils and that worked just fine, but for some reason the 791XV won't detect the tach from that connection, i've thought about using diodes to connect to the tach from several of the coils, but haven't tried that. Any ideas? THANKS!