About SPDT, DPST, DPDT and others:
The first 2 letters SP or DP are referring to single pole or double poles. This is the very same as for regular manual switches. Single pole is the most basic with a single common terminal and a single normally open terminal. You will find single pole and double poles relays but single pole relays usually only have a normally open (NO) contact while double poles relay will have both a NO and a NC contacts along with a common contact.
The last 2 letter (ST or DT) are referring to single or double throw. A double throw (DT) relay is simply 2 single throw relays mounted together and activated by the same coil. You can of course use only one set of contacts which will result in the very same thing as using a single throw relay. (same as PCW drawing)
If you do a search for 'arduino relay' you will also find multi 'channel' relays. Those are simply multiple relays mounted on a single board. Each relays can be SPST, DPST or DPDT. (Note that most arduino relays are 5V which will NOT work for this application)
Here is an example of a 12V relay that would work for you:
(ref:
www.amazon.com/HiLetgo-Channel-Isolation...rigger/dp/B00LW15D1M
)
The contact on the left are NC COM and NO and are rated 10A for up to 30V DC. Well enough for this application
The contact on the right are DC+, DC- and IN. This specific type of module require both DC+ and DC- because it has a led to indicate if it is activated or not and also because it can be activated by a low (gnd) or high (12v) signal. Although not written on the relay itself the description on Amazon specify that this is a 12V relay, meaning that the voltage needed to activate the coil is indeed 12V. The IN contact is where you will connect the "7I77 ENA+".
You can also see a little jumper with the marking "L" and "H" allowing to have the relay activated with a low or high signal. I believe that in this case you want the jumper to be on the left side (L).
