I think the problem is the 8 flashes. Means there's a connection (CAN ?) line error from what I can make out. I came to the conclusion it was because the siren box was triggering by itself without being commanded by the alarm part of the body computer. The body computer knows an alarm wasn't triggered but the siren is operating so flags a CAN line error.
On my car with the siren box connected the alarm goes off randomly when it's armed with the key fob. Using the key fob to disarm doesn't work, just unlocks the car but the alarm carries on regardless until it decides to stop when it feels like it. Means you can't use the remote to lock the car since there's no way to stop this arming the alarm as far as I can make out. My solution in the end was to simply unplug the siren. This stops the false alarm triggers (no flashing indicators) when the car is locked with the key fob (alarm armed) confirming the siren is the problem. The problem could be related to the fact the siren contains a battery so it carries on sounding even if the car battery is disconnected. I'm guessing this battery doesn't last forever so perhaps when it starts to die it causes the siren to do odd things causing false alarms. The fact your siren only produces a faint alarm probably confirms the siren box isn't working properly.
Last edited by Alexie; 18-12-15 at 16:57.