Gary, I posted this also on your other message, but I think this is probably the right place.
The symbol you referred to as a T with dog-ears is NH's version of the ground symbol. NH, like automotive manufacturers use such a connection to the tractor frame to complete the circuit, rather than running another wire back to the battery. Since the negative side of the battery is also tied to the frame, this completes the circuit.
The other main thing you need to understand is the connection of wires from one page of the wiring diagrams to the next. If you note in the lower-left corner of each page is a "Frame #". This designation is used throughout the diagrams. On every page (frame) there are references in a box such as FR.3, D. This means this wire (HM-31-BK-18), which is on page, Frame-1, connects to a similar point on Frame-3, point D. If you look on Frame 3 you'll find a similar box with a FR1, D, label.
My suggestion is, if you want to understand the electrical system completely, start on Frame 1, where the battery, G-01, the alternator G-2, and the other main system components like the starter, main fuse, and other parts are located. Then branch out from there. Note the wire designations, which carry on from page to page. These are further explained on Frame-8. (Just a note, I see I gave you the wrong color code for T, as it actually stands for TAN). Good luck with your new toy, er ah, essential piece of equipment. If you have further questions, I'll do my best.
Also, this wire everyone keeps referring to is a pair of wires you will find in a connector under the right hand side gray plastic 3-point control housing to the right rear of the seat. It is tucked under there along with the wire to the right rear flasher. However, this wire(s), designated as HC-082-BK- 14 and HC-049-0-14 (on the right hand side of drawing Frame-4 ) for S-10 and E-14 may not be adequate for what you intend to do. These are 14 guage wires, which are capable of handling 15 amps, or 180 watts total. Usually, as shown on the Frame-4 drawing, this wire requires an internal switch in the lamp. If you go the ROPS route, I'd suggest you look through the drawings for another place to pick up power, either through an existing fuse, or add one and then switch the new lights at the dash in one of those spare rocker holes. Whatever you do, make sure you've adequately fused it. Good Luck.