how to connect many sirens to relay

also i'm not familiar with the unit you have but on most dei units the 508d is plug n play, i'm not sure about your 509u, someone else might help out there.commit your way to jehovah and he will act in your behalf. psalms 37:5

What's a 509? If it's a sensor, they can be parallel wired to a single port.  The blue and orange wires should be dioded before joining with the bands away from the alarm.  Why so many sirens?  You would have to add at least two more just to double the sound pressure, a single set of air horns would be more advisable if you want to hear it.

See my post above and read it again. The sensors themselves should have these instructions in the packaging.

I would honestly stick with the tilt sensor, prox sensor, back up battery, one internal siren and 2 external. There is no need for a glass breakage sensor given that the prox sensor will initially trip warn away if someone is close to your car, secondly if they do break the glass and reach in the vehicle they will trip zone 2 full alarm on the prox sensor.  The 509U works similiar to the 506t glass sensor. it will sense the pressure change upon breaking the glass..where as the 506t uses frequency detection of glass tampering.  I guess you have to decide which one you want. This will eliminate your dilemma. Personally I have the 508d prox sensor.  The blue wire from the 508d is tapped into the green of the same harness thus freeing up a blue wire to the brain, which is what I connected my tilt sensor to. Having one internal siren should be fine. 2 external works for me. I have one under my front headlight, and the other under the rear tail light up in the bumper. Both inaccesible.. but if for whatever reason one gets eliminated, they still have one more to get to.  Too many sensors and too many wires can be a headache if you have problems down the road, false alarms, and of course more wires a thief can trace back to you brain and dismantle it.. that is if they are good and know what they are doing. Just my thoughts from experience.