I have been meaning to update this thread. I am ready to explore the addition of a crank trigger to my Howell system. Before I call Howell and ask them if they can point me toward a hall effect type sensor that will produce a signal that the GM computer can read....... Can I measure the signal voltages at the ecm input port with a multimeter? I'm thinking probing the ECM -RPM input terminal with the engine running? Ive searched the web to find what the desired GM ecm input voltage is but haven't had any luck.