The car is a '96 S420 fitted with an Audio 10 cd player. I am trying to figure out how to get the VSS - speed sensitive volume control to work. The wire is present in the harness, I've tried voltage measurements and get some fluctuations from ~0V at a stop to ~6.8 - 6.9 at speed. I don't have an oscilloscope to measure frequency.

The radio has the feature. Is there something else needed to activate it?

The dealer can turn it on and off. This is assuming that your radio actually has the feature. The sales brochure for my car says it has it but the radio manual does not and the dealer said mine doesn't. The dealer said most people don't like it anyway. I know that the volume change increments were adjusted over the years to smaller amounts.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra