viper siren output malfunction

I have searched the forum and can't seem to find an answer. I installed a Viper 5704v into a 2007 f-450 wrecker. Everything works fine except the output for the siren wire. When the siren is hooked up as it should be, only a muffled tone comes out, no confirmation chirps, nothing and it stays on constantly. I checked the output with my probe and get no signal, when testing with a volt meter, it reads 12v. No readable change when the unit is armed/disarmed/activated. I have never come across this problem before and can't seem to figure out a solution.

Just a note, the siren does work properly when hooked directly to the battery.

When the siren is connected to the output wire, the voltage drops from 12v to about 1.2v and when the alarm is triggered, there is no output from the siren wire and the muffled tone stops.

Need to check your main power and ground to the alarm. And always run grounds together, ie ground siren to alarm brain ground.

Or the siren output chip has failed or the siren itself. Connect 12V+ from the battery to the red wire and ground the black.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
Read the installation manual, do a search here or online for your vehicle wiring before posting.

I checked and rechecked all of my connections. The power input is connected directly to a constant in the ignition harness and I made a new ground with a cleaned connection. The siren does work when tested on the truck's battery. I think the circuit may be bad in the unit. Luckily, the truck belongs to a friend of mine, so he was happy with hooking up the horn wire and I gave him a set of truck air horns I had in stock in the back to make it louder for him. He cared more about the remote start function than anything else. If it had been a normal customer, though, I would have had to simply send the brain back.