No matter what harness you have if you just want to know how to wire back up lights: Hopefully you have an extra fuse. If so, that fuse should already be hot on one side. Wire other side of fuse to one side of back up switch, other side of back up switch to light bulbs. Put a fuse in the slot...Done.
Let me know if you don't have extra fuse....but you should have if you have extra unused wires. Pick any unused fuse. Most of the fuses are supplied power from the ignition switch.
If you have extra wires, coil them up with tie wrap and stash up under dash....or disconnect and save in a drawer.
I can't tell by your post if you JUST need one more thing (the B/U lights) or other circuits. If so, let's take one at a time.
My question is, were you supplied with a schematic or wiring diagram? If so, what does it show for temp gauge hook up and etc.? (that should be the EZ part of the EZ kit). If you call them, I am sure they will guide you on exactly how to wire any component that the kit was designed for.
Basic gauge hook up, as described by others already:
If the wires "coming thru firewall" are coming from the sender, they go to sender terminal on gauge. If they are from senders they DO NOT GET POWER! The gauge has a positive terminal which gets hot from a fuse, which gets hot from the ignition switch, which gets hot from battery direct. The ground for a gauge is usually by a path thru the mounting bracket to the dash to the chassis. Some gauges also have a light which is wired to dash lights, I believe.
I would assume your fuse block was pre wired and has wires that need terminated to switches and gauges to supply fused power. These wires are marked as to what they go to or color coded to the schematic or wiring diagram.
Don't get frustrated, just do one circuit at a time, we will help you. Just make sure you keep up with your post.
