508d proxi turn off when car is running

I have just recently installed the 508d proximity sensor. It works great and adjusted it to where i want it. I go out for a drive and my radar detector goes crazy almost all the time, mostly k band.
What i want to do is cut the power to the proxi sensor when ignition is on. Using a relay, the only way i think i can get this to work is:
85 - ignition
86 - a ground with a resistor (such as a 12v light bulb)
87a - 12 volt
30 - power wire on proxi.
87 - nothing

my thinking is that when the car is on, 85/86 makes the switch activate 87 and and 30 which will have no power to go to the proxi.
When the car is off, there is no current through 85/86 and therefore 87a/30 stays connected sending power to the proxi.

Are there any other ways of doing this without the resisted ground?

If wired correctly, the 508D is not normally powered up when the ignition is ON. You are not really on the right track at all. It will be much simpler to do. But first...

What alarm do you have the 508D connected to? How is it currently wired?

The python 881xp. The proxi sensor has 4 wires. Red, black, green, blue.
I tagged them into the shock sensor wires which are Red, black, green, blue. The proxi works fine but my radar goes off randomly, every 15seconds to 1 min. I killed the power to the proxi and drove around for 20 min and i did not have any false alarms, especially not every 15-60 seconds. I live in the suburbs and i was not around stores or anything. I noticed this problem the second i got in my car after installing the proxi cause the radar was going on and off in my driveway. Even though the proxi is not armed, it is still receiving power cause it is sending radar signals. Look at the shock sensor while the car in on, the led inside blinks when getting shook around, so obviously that power stays on.

You shouldn't tap onto the shock sensor harness for power for a 508D.

Connect the orange ground when armed wire in the primary harness to the 508D ground input. Tap the power input of the 508D to the 15 amp power input wire also in the primary harness. You should then connect both the green and blue of the 508D to the loose green wire in the shock sensor harness.

that makes sense, this way the proxi is only on when the system is armed. When the car is running the orange ground is cut off, therefore the proxi does stay on.
Thanks a lot for your help.