Ok, I took some pictures and maybe if you're confused this will help you out. I purchased a add-a-circuit found here.
I used a hardwire kit got this one from ebay
. I cut the positive side and crimped on the end of the add-a-circuit. I also removed the ground and installed a similar larger diameter end.
I then ran the wire up the side a-pillar and tucked the wire in between headliner. I was getting sick of the old suction cups so I just 3M'd the mount in the dot matrix section so the detector isn't visible from the outside
These are the two plugs all the wires are coming off of. On old cars all the wires were directly behind the fuses. If you push the tabs on the bottom you can move the box around and see the back. There are no wires visible. Therefore before you could just look behind the fuse and you could see what color wire to splice into.
You can see the plugs on the other photo. These are the wires you would "tap" into.