Alarm connections

Hi, i'm trying to install two add on sensors to my alarm, a 507t tilt sensor  and a 508d dual proximity. The problem i have is that they require a negative switch from the alarm to arm, my alarm gives a positive switch am i correct in thinking i can us a relay to take the positive switch and energize#86 on  the relay and have a negative feed to #87 and connect the sensors to #30 on the relay, giving me a neg switch. How do i stand about having to fit diodes to the relay and the sensors?

Hey, check out this page. It tells you how to convert positive to negative using a relay. And yes, if you're hooking these sensors up to an existing sensor, or if you're hooking the two of them up to the same wire, you'll have to diode isolate each of them.

My only concern would be (since I've never had to convert the + to - like you're doing) would be that the relay would have to stay energized the whole time the car is off (to keep the + signal to - signal going). I'm not sure how much current that would be drawing. Maybe someone else can answer as to whether or not that's bad.

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Thanks for the info, i think a relay coil only takes about 200ma to energize it, so not to bad. I may be wrong so any other info would be great.

um..... correct me if I'm wrong...but doesn't your alarm, like most I've installed, in fact, all of them, put out a negative constant for the starter kill relay input>?  this usually orange wire, can be diode isolated to power up accessories such as the ones you're trying to employ.  Feel free to  bash me if I'm wrong... although I'm usually not..

Good point....that sounds better than using a relay.

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The alarm i have fitted is a GT Auto alarm, it came factory fitted to my Focus RS and is a Thatcham cat 2-1 which means it is an add on to a already immobilised car, so there is no need for a feed to a starter kill relay, but thanks anyway for the input.

strange..... I'm trying to think of the last time I saw an alarm without a (-) output when armed...... NEVER

I think you may be reading the directions improperly, sensors don't require (-) inputs to become active. Most tilt sensors only have 2 wires, one ground and the other is a neg. output. The proximity sensor usu has 4 wires: 12v const., ground, and 2 negative outputs(one for pre-stage and the other for full output). If your alarm has an external impact sensor(dual stage) you can just tap into the 2 trigger wires at the impact sensor.
Hope this helps.

The tilt sensor i have tells me i need a (-) input because everytime you arm the alarm it sense's what angle the car is at and any change from that angle , +1 degree sounds the alarm. If it had a constant (-) and you parked on a hill it would think it was getting jacked up.

I just had a thought, could i use the (+) switched output to turn on the sensors and have a constant (-) or would the current draw be to much for the alarm?

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.