corolla 00 car alarm led

I was trying to add a led indicator for my car alarm, looking at the transmitter the alarm could be a prestige PRO9445FT or PROOE2KDX there is no model number on the alarm brain.... I found the original led hidden behind the dashboard. My idea is to install 2 leds rigth next to the each front door pin (like the ones audi's & volkswagen have). I bought 1 12v flashing led from autozone but when I connect it to the "original led" from the alarm the extra led blinks in a different pattern. I'm not sure if i can connect them like that. Another question the black wire coming out from the alarm is the antenna?? can I connected to my car antenna to get a bigger transmitter range?? All comments are welcome.