This is my build if you make one you are doing so at your own risk. I am showing you how I do it. If you copy my example you are claiming to have the skills and safety knowledge to do so. This will be done as a visual aid to how an STC-1000 is wired using two external relays to handle our heavy heater loads. This step by step is to be considered as a visual wiring diagram. If I was to do this as a working assembly I may need to make my wires longer, etc. I am doing it in such a way that makes it easy to see and follow. This is a valid method but I do not have to do it exactly like the demo pictures as long as I make the same connections. I am going to show how I would build the circuit if I was not going to put it into an enclosure to make it easy to see. This is the relay I will be using: Search results for "70132401" - Allied Electronics Here is one of many links to the STC-1000 that I could of used: All-purpose Temperature Controller STC-1000 Auto switch between refrigerating and heating - Amazon.com About the STC-1000 The STC-1000 is a thermo control unit that is used by the thousands in the food, brewing, and manufacturing industries. It is very reliable and accurate. It reads in C and will hold a reef tank to within about .6Â° C if you have enough heater and cooling capacity (this is "about" barely over 1Â°f). You can get this device delivered to your door for $35 or less because of the quantity they are manufactured and sold in. Since I live in the US I was careful to find one shipped from inside the states. I was also careful to buy one that is designed to work at 110VAC (wall socket) because they come in several voltage configurations. The STC-1000 comes with the 6' temp probe included in the box and a set of instructions that take some background in this type device to understand easily (if you get my drift). I will need some 14 gauge wire. I will use two colors. (I only need a few feet) I will need some 25 gauge ( I will call this wire the light gauge wire) or similar sized wire in three colors. (I only need a few feet) I will be using a terminal strip but it is not required, I use it because it makes it easier for me to demonstrate how I wired it with more clarity. I will be using some forked terminal ends and two sizes of female spade quick disconnect ends. I will be using two cheap, 6 foot, three prong, multi-socket extension cords rated for at least 10 amps. Not shown are the light gauge wire, wire nuts, .... and the female spade connectors only represent the three kinds I will actually be using from my kit. Here are most of the parts I used laid out.