basic question, on 86+ birds, and in 90+ camaro's do the VSS's in the tranny get any sourced power. switched or constant? They have two wires, yellow and purple....which one of these wires is signal, and which is a ground, just curious, or is one of them a power wire.

Another Question

on 85 and earlier birds, or the later model maros w/ a cable speedo, does the VSS on the back need power? Not the yellow box that is essentially a "mini-buffer" box (i'd think) as i know the electronics in that box would need power to convert the signal...but what about the actual optical sensor. It seems kinda pointless to have a red, black, and green wire going from the optical sensor to the little yellow box, if there's no power needed at the sensor itself. Anyone have wiring for those parts? I'd love to see a schematic.

 

On the earlier models with the little yellow box, yes it gets power. It's an optical thing. If you look into the back of the speedo itself, where the thing is mounted, you'll see the part that the cable drives, which actually is a magnet; it looks like a little bar from the rear; it's shiny; the speedo piece right in front of it, that looks like a little drum and is attached to the pointer, is black. The yellow box has a LED and a phototransistor, that literally "looks" at the shiny / black alteration and makes pulses out of what it sees; 2 pulses per revolution.

 

"on 86+ birds, and in 90+ camaro's do the VSS's have power", no, the VSS itself is an A/C generator. It has a coil of wire with a magnet that rotates inside of the coil. Both wires are signal.

The ECM measures the frequency of the signal to derive the vehicle speed.

RBob.