Alarm connections

As long as the output from the tilt sensor is going to the alarm it doesn't matter. The alarm will only activate when the system is armed, so if the alarm is off and the tilt sensor is sending a neg input to the alarm the alarm will just ignore it. Besides, from what your telling me, the tilt sensor judges movement relative to its own position, so if the system is armed with the sensor tilted(parked on an incline) the sensor will only trip if movement occurs greater than the present angle.

I've hooked up three sensors parallel with my shock sensor inclusive.  I had no adverse effects.  Most sensors do draw very little.  I do know, however, that the proximity detectors do draw significanlty more than a shock sensor and if left on will have the propensity to drain a battery dead in a noticible amount of time.  Make sure and diode isolate.   One thing to keep in mind is that I have seen a lot of alarms with the shock sensor still active whether or not the car was armed and even when the ignition is on.  I suppose you would need to verify a switched output.  But I do usually wire up my sensors wired hot and activating with the ground output of the alarm.   I still can't come to grips with the fact that you have an alarm with no neg. output. 

Thanks for youe input, will let you know how i get on.

Just been reading up on the proximity sensor it says you can us a latching relay to supply your (-) when armed supply. I have not come across one of these before, can someone explain how they work.

I'm not sure a latching output would be your best bet as you would have to physically press the auxillary channel button, which usually activates a momentary (-) output used for a trunk pop or the such, but can be converted through programming to latch.  But you would have to remember to set it everytime you wanted to use it.