wired correctly, whats the issue then?

Ok so I've had my alarm installed for about 2 years.  Its a Dowentec pushbutton/alarm, S Korean brand.  I have 2 sirens installed, one in the engine bay and a piezo under the dash.  Over the last 6 months the one in the engine bay has been working half the time, it would only chirp half of the chirp.  Finally it stopped working and I figured it went bad for one reason or another.  So I tried another siren a buddy had that I know worked, still nothing, so I tested the old siren on a battery and its still good. 

I tested the wires at the siren and don't have any voltage and figured the output might be bad but then the other siren shouldn't work.  I'm wired this way; brain to a relay to the siren in the engine bay, the 2nd piezo siren is tapped into the wiring after the relay. 

I tested voltage at the tapped wire and have voltage before and after, however nothing after the firewall.  I cannot see where the wire is coming from the firewall if there is a cut/splice/grounding out.  So my question is 1) Am I wired correctly for the 2 sirens?  2) Can I run a wire from where I know I have voltage to the siren to make sure it works and if so keep it hooked up that way?