I am wanting to install a new transformer for my alarm system. The old one was taken out by a friend and was incorrectly installed according to him (an electrician).
It is a 16.5 V transformer which sat at the bottom of the panel. It has 2 black wires coming from it. There is a place to screw the transformer into the panel at the bottom. I am assuming one of the black wires goes into the main ground bar. However, where does the other black wire go? How does the alarm system setup? This is an older type alarm system.

Is there a place where I can find diagrams for alarms? No spam please!