I made a conversion to an aftermarket alarm bij making a connector box.
This way you can always switch back or take out your alarm when you sell it.
Because you're using the original connector on one side.The pins originally in the factory alarm can be outsourced and soldered to the aftermarket wiring.
Fitted it when I got my vx and it's been working flawlessly since.
I used a texalarm bas328 system, but i don't know if it's available in the States.