ok I just bought a pa/siren system to be annoying with lol. anyways It came with three wires a speaker wire which I ran through the firewall into the mounted speaker in my bay. then I have a power and ground wire, it needs 12v only when ignition is on so could I wire it into the accessory outlet like for phone chargers I never use it? and how would I wire it? also where is a good ground under the dash? thanks

 

Just splice into the power wire for the outlet. Plenty of spots under the dash to attach a ground wire. Usually any metal part will work. Use a meter and check continuity to a known good ground if unsure. Then a self tapping screw to hold the wire end.

 

do you know if that outlet shuts off when the car is off so it doesn't drain the battery

 

Not sure but you could check with a meter. Or plug your phone charger in it and see if it has power with the ignition off.

 

Find a power lead in the fuse box in the cab(pre fuse). You can tap into one of the ignition switched leads(use a separate inline fuse for it). I would check the amp draw on it before you anything. Might need a seperate relay in the engine compartment.