DEI sensor, Compustar alarm

I'm having some trouble connecting a DEI 508D radar sensor to a Compustar 3300 alarm. First I tried splicing it in directly with the shock sensor, this messed up the shock sensors power wire and so now I run it off a constant 12v (I know I should have isolated them with a diode but this approach has worked on other alarms in the past). The shock sensor works fine. Next I tried connecting the radar sensor as follows, constant 12v, 2nd stage input on alarm, 1st stage input on alarm, ground when armed from starter kill output. Again I think I messed up the alarm, this time the ground-when armed output. The starter kill no longer works (car starts up when the alarm is armed and even when the alarm is triggered). Next I tried using a chassis ground for the sensor, just to see if it will work with this alarm. The lights on the sensor responded to motion, but the alarm didn't trigger or warn in response to the sensor. So I cut the sensor out, and touched the alarm's 2nd and 1st stage inputs to chassis ground, and the alarm responded with a warning and a full trigger respectively. I know I was stupid to rush through things without running to the store and getting some diodes to do it properly, but like I said, it has worked on many alarms for me in the past (Omega and DEI). This is my first Compustar. I checked the circuit board and there is no obvious damage. What can I do to salvage this situation? How can I get the starter kill working and is it possible to use this sensor with this alarm? And I know the temptation to flame is there, but please restrain it. We've all been rushed into cutting corners when we shouldn't.

This is how the sensors are hooked up now. Both sensors have a constant 12volts. The shock sensor is using it's original 1st and 2nd stage inputs and ground when armed. The radar sensor is using the alarm's extra 1st and 2nd stage inputs, and has a diode with the stripe facing the sensor on the ground wire spliced into the shock sensor's ground-when-armed wire. I also tried connecting the starter kill ground-when-armed wire with a diode, the stripe facing the starter kill relay to the shock sensor's ground when armed wire. It didn't work so I cut it out of the loop. The shock sensor works great. The starter kill does not work. The motion sensor does not seem to work. It's adjustment knobs are in the center.