Dash cam install - which wire is always hot?

CB post? If not you'll have to find one in the fuse box.

 

You can check the cigarette lighter outlet

 

I have a dash cam as well.
The only reason you would want constant power is if you're using the parking monitor, which on most dash cams can be turned off.
If you use the monitor make sure to go into settings and adjust your sensor, otherwise, everytime you get rocked pretty hard in the wind, truck gets bumped, etc., it will snap a picture and lock the file.
That can chew up your available memory for recording in loop pretty quick.
If you don't use the monitor, your cigarette lighter plug will come on when you start the truck and begin recording.

 

I have a 128gig Memory Card in mine. I never shut it off.

 

What kind of dash cam do you have?
Most of them I looked at online could only go 32g. The one I got can go 64g.
Don't remember seeing any that could go larger.

 

That's ridiculous in 2017.

I just got a
Street Guardian SG9665GC v3
They say up to 200gb.

Even my old one could take 64 gig Cards.

 

Mine has 64g, but I'll look into Street Guardian.
That name doesn't ring a bell, but definitely worth a look if I can go more than 64.