Subd for future use...
try without relay on just the white wire indicated in first post. i don't recall if it's twisted worth a green wire or not. i doubt there's a difference in trim vehicles as long as it's the same navigation head unit.
The relay I used is actually a smaller, more stable board mount relay meant for integrated circuits. It has one coil but two separate NC and NO pairs. I used a 220 ohm resistor in line with the coil to lessen the current going to the relay. I did kind of the same thing on my tailgate lock mod since the actuator was driven very hard to turn a small lock.drop resistor or diode? there should be contacts labeled if its a standard automotive relay like a bosch. 85, 86, 87, 87a, 30.... that kind of thing. those relays can be tricky with finer electronics. I understand the desire to have a lighted switch, but consider youd know pretty quick if you forgot to flip the switch because your location wont move on the map.
I would really consider finding the pin out for that particular model head unit. not doing so could lead to problems and even damage. you could test the wiring more accurately with a multimeter, the vss should be ac and fluctuate as the vehicle moves, not just rpm's in neutral. you could only tap into the white or green or whatever color you think is the vss and attache multimeter to it, drive and watch it rise as your speed rises consistently. if it doesnt then thats not the vehicle speed sensor wire.
I have nothing to lose so I will try test with regular switches on the white and/or blue wires alone. I will try just the white first. Who knows maybe the relay contacts are picking up EMF and sending it to the VSS somehow.right on. seriously just try the vss on a switch. pull relay out, its a neat idea though to have a lighted switch but may be more work then necessary.