"There is nothing electrical tied in with your mechanical speedometer"

That's what logic tells me, but then I'm stuck with the fact that while the speedometer was out of commission, no fault was displayed. Within minutes of the speedometer's repair the fault shows up again. It's a curiosity more than a problem. I posted the problem with the "13" code before. At certain engine speeds the check engine light comes on. If I let off the gas pedal it goes out. If I tromp on the gas pedal it goes out.
And when the code is read it is always "13". The sensor is less than a year old, it wasn't wire rigged (exact replacement). I've traced the wire and there's no apparent break or current leakage. This business with the speedometer is the first clue that it might not be the sensor itself.
I just can't connect the dots to figure out why one would affect the other.