Exactly what shadow said, except I didn't ground the third wire. The negative is already grounded so there is no need to ground the third. You can do it if you feel safer. Mine has been hooked up like this since July without a problem.
I just spliced the stock signal wires to the hella wires. I used a tester to find out which was positive and negative. There is no other way to really find out except for experimenting and possibly blowing a fuse or two.
Use the brackets like shadow said and test fit the brakets to make sure you have clearance. I also used metal washers to bring the signals a little farther down. If I didn't do this, the upper portion of the signal was hidden behind the bumper. The washers were also used to level the signal. The part of the rebar where I mounted mine was slightly curved so the signal didn't sit straight. I think I used 6 washers on one side of each signal and 3 on the other side which let them sit straight.
You can see the signals in the side vents here:
Mark
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94 Prelude VTEC - garage queen - SOLD

03.5 Titanium Grey Mazdaspeed Protege - new garage queen
07 SSM Fit Sport - daily driver
AIM: MarkSpeed94