Trailer Protected?

 Hi,

 How can protect my trailer ( JEt Ski), So when the plugs for all the lights going to the trailer is unplug,  this would activate my car alarm?. My alarm only offers one motion sensor and I would like to keep that in my car. I got a ground going to the trailer, is there a way that when this is unplug it will set my alarm, if my motion sensor wont p- it up?

 Thanks.    

Try a pull up:

Ground a wire in the trailer, run it (in) to the vehicle. In the vehicle, run a ( different) wire to +12volts , run this wire through a 10 K resistor, and connect it to the wire comming from the trailer. connect the wire from the trailer to the + alarm trigger.  The wire from the trailer will 'hold' on ground until the ground is taken away ( thief disconnecting the trailer), when the trailer is disconnected, the +12 volts will be sent to the + alarm trigger ( setting the alarm off).

You may want to add a switch, so you can turn off the signal going to the alarm, when the trailer is not connected (when you are not using it).

good luck :)