I have looked into this a lot since I am on my third Rover fix on this issue. My Foxwell 510 scanner found an ABS fault that indicated a SVS electrical fault. This led me to Josh's fix but I needed to convince myself how the SVS switch worked and since I had working Rovers to compare good and bad switches I went to it.

I used this procedure to VERIFY the SVS switches being good or bad or was it the switch wiring to the actual switch that was bad. So here it goes. Simple. All you need is a ohm meter, a person to press the brake pedal and pop the hood, turn the engine off.

One lead of the ohm meter goes to the battery negative (or validated chassis ground). The other lead of the ohm meter connects to the green/yellow wire of the Wabco modulators black connector (second row of wires, end wire closet to radiator). Remove the black connector and measure the corresponding pin at the Wabco modulator. The reading should be around 3,000 ohms (3k ohms) with the brake pedal not engaged. If it is zero ohms you have a short inside SVS switch - remove/inspect/replace. If it is higher than 4K then you have an open (bad SVS or open internal wire). Press the brake pedal down and the resistance should drop to 1,000 ohms. If not then one or both of the SVS internal switches are bad - replace SVS. If the reading changes to 2K then one of the two internal switches are bad - replace SVS. If the readings are 3K with the pedal up and 1K with the pedal depressed then the problem is NOT the SVS switch - no need to remove or inspect.

Let me know if it works for you.