I bought my 05 Scion tC used with the first owner has done quite a few mods to, one of them being a Viper Alarm system.
I have no idea how these work and I don’t have a key fob but I found the main controller and everything seems wired up.

But is there a diagram or something I can look at to possibly figure out how it works?

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You need the model number off the alarm. Once you have that you can look up what remote works for it on Directed's site.

https://www.directed.com/

 

It's a Viper 5901 and my car wont start if i unplug it, but it i don't see any flashing lights on any part of the system. I really wish i had a FOB for it. it would be cool to use remote start.