Hello I have a 78 cutllass supreme and a 84 monte carlo with the same set up as those, first if you look at the ign. harness for your car (key switch) you should find a wire for 12 volts, use a multimeter or test light to verify...
The 516L and the 791xv has to be connected completely, the blue wire of the alarm (791xv) and the 516L share the trunk wire, or hood whcih ever you prefer... the green wire off both units MUST be used for neg. door triggers..and for the prox. snsor since it can send a ground trigger it can be hooked up to the door trigger as well but make sure you diode isolate from the other wires you never want to run more than one mod. or brain off one wire, ex. off the orange wire if you connect and external relay for starter kill, and a Varad led light you should diode isolate from each other to eliminate the prob of interference.... and on the 791xv and 516L to hav the unit talk when remote starting connect the 2 pin plug into the (516L) unit and the two wires (ORANGE / black) and (blue/black) the O/B connect to theneg accessory output of the 791xv which is on therelay sat. ribbion harness, and the wire is (orange) and the (blue/black) wire connets to the blue wire of the alarm the same location of the orange wire on the sat. rib. harn. , well have fun...
-------------
Thats SIK!!!!