Directwire says green wire at the ECM, and there are about 5. Tested all of them and the only one that seems to have a chance of being right gives me about .5 volts when stopped, and just over 13 volts when moving. Theres almost no transition. Is that the right wire? Its the first time I'm wiring into a speed sensor so I'm not sure. It just seems like voltage should increase with speed.

Thanks in advance...

voltage doesn't increase with speed. The fequency increases with speed. Though what you tested sounds about right for an older gm truck.

Thanks, just to be sure I"ll check the frequency tomorrow