I made this analog circuit for two reasons. One: To stop my wires from melting due to too much current. Two: To limit the load on the alternator. Instead of the lights on a trailer going through the tail light circuit on the vehicle, which caused mine to melt, It will pull current directly from the battery using relays to switch. The entire circuit is 12V operated. Contains three 12V inputs, two 12V outputs, one Negative input.

These pictures show the circuit and some melted wires similar to what I had to replace.

Step 1: Components & Materials Needed

Components:

A PCB soderness board (I reused one that I had bought for something else 10 years ago)
2 automotve 12V headlamp/taillight relays 10Amp
2 1000 Ohm (1K ohm) resistors
2 LEDs, 1 Red, 1 Yella (2V each)
An assorment of short wires (14 guage) and for the LEDs any small guage will do.
2 10 Amp fuses doesn't have to be automotive but it is easier to work with.
Wire connectors (Male/Female assortment)
A DPDT slide switch to turn off when not in use.

Materials:

Soldering Iron and RA core solder to stick
A pair of helping hands will help with alligator clips
A drill to widen the PCB board holes to take the more larger components
A lot of patience because these things are small and in a crampt area

The picture of these cool components courtesy of Google Images, and two pics of the underside of the circuit, here you can see where the patience comes in.

Step 2: A Demonstration of the Circuit

In this video I show you how this circuit works. And if you would like to see my other videos check out youtube: Accord8922 or Instructables via Florlayamp (my bro).

And The schematic of one side of the circuit: (You might have to blow it up to see it better)

Step 3: Setting Up Some Wires in the Truck

Its a mess of wires that had to be redone a few months previous. But I had already set up some wire connections then so all I had to do now is add a power, negative and tap in two of the light wires. I ran a wire from the (+) side of the battery all the way to the back for this device as well as for some auxillary power for when this is not in use. With this having been done its just as simple as plug and play for anything I want to connect back here.

Step 4: Making a Housing for the Device

I figured this thing being somewhat fragile needed some protection from anything that may come in contact with it while its connected. I had this old jewelry box not being used to I cut it in half to the size of the deivce leaving the window part and door still attached to see and opertate it. I mounted the board with a wood dowel from a foam paint brush and screwed it into both the board and the box. I'll have to figure out something to cover the open side later. With it nice and firm and the wires accessable its ready to mount and enjoy.