power door locks

If it doesn't have factory keyless, the locks are reversing polarity, also known as 5-wire.  You'll need to get two ordinary SPDT automotive relays.  The Audiovox manual includes wiring instructions, and there are some on this website too.

The lock wires on that truck are a bit hard to access...here's one way to do it.

Locate the boot where the wires run into the driver's door.  On the side that goes into the car's body, pry the boot out; it has two white plugs...... pry the plugs out, and then pull the wiring out into the door hinge area as far as you can.  Run your new wires out to this area.  Perform your work while the wires are in this position....... make the connections on the "body" side of the plug, not on the "door" side.

When you're finished, push the wiring back into the hole on the car's body, where it will now be safe from the weather, and then reattach the rubber boot.