Here is my follow up on my problem as I finally got it fixed this weekend! Because I struggled finding folks with much knowledge on this particular issue on forums, I've decided to make a good effort to add my lessons learned on this.
First, after taking the plastic on and off my quad twice now, I've decided that I HATE DOING THIS TASK. It is neither easy or fast. After doing it twice now, I've gotten better and faster, but it is a pretty time consuming activity with the included necessity of pulling my after-market bumpers and gear racks off. I was also forced to take apart the headlight/speedo pod as well, adding to the work. This was definitely necessary as I needed unhindered access to the cable harness, also known as a wire harness, cable assembly, wiring assembly or wiring loom.
My initial checks based on looking at the wiring diagram focused on continuity and voltage checks at the speedometer/display pod and the battery.
First, I did a continuity check to ground...all good there. My second check was the main power from the fuse box to the display pod. It starts as a Red with Black stripe wire at the fuse box and changes at a crimped junction in the wiring-circuit to a Red wire at the pod. Eureka!! No power was making it on that circuit to the pod! Curiously, there is more than one power source into the pod, as the back-light had always functioned, but nothing else.
At this point, I decided to bypass the suspected damaged wiring circuit and used spare wire I had straight from the battery into that wire in the back of the Speedometer Pod. Yes! It worked! As soon as I applied that power, the pod display came fully to life, including the gear selector lights... To say I was happy is an understatement.
Now all I had to do was track down where the break in the circuit was. With all the fender and body plastic removed, I started tracing back from the Speedometer Pod toward the fuse box. Power was present at the fuse box going into the wiring harness. Starting at the front was just a guess. It was necessary to strip off the wiring loom tape covering and all the zip ties that held it to the frame as I went back.
I found that Suzuki uses crimped brass connectors in the wiring harness to form circuit junctions with multiple wires. I had seen this on some autos before, but I personally like all such junctions to be soldered for circuit security and reliability. I immediately suspected one of these junctions would be the likely problem. As I encountered each of these junctions on other circuits in the wiring harness, I took the time to strip off the clear tape, inspect, and solder them so they would not be a problem on the other circuits in the future.
Eventually, I came to the junction where the Red wire from the Speedometer Pod spliced into three Red with Black Stripe wires. This was located just below and in front of the air box along the frame on the left side above the motor (what would be the fuel tank location on most quads). It was immediately apparent this was where the break was as the Red wire fell out of the package of crimped wires. After I stripped away the clear tape, I could see it was corroded and the brass had actually turned green from oxidation. It is not clear what caused this particular junction to corrode while none of the others I encountered had any signs of corrosion (about 6 total that I soldered).
All I did at this point, was solder the connection back together and cover it with heat shrink for good measure. A quick test showed the display now functioned properly with the repaired wiring harness.
Last steps were to re-wrap the wiring harness with high-quality electrical tape, re-attach the harness to the frame with cable ties, and re-assemble the body and speedometer pod assembly. The hardest part of the job was, once again, reassembling the body. I did take the time to cut an access hole to the oil fill/dip-stick which is inconveniently located under a plastic panel on the left side of the quad by the left foot rest; as well as cutting the hole where the wiring harness comes in from under the seat a little larger to easy assembly and future dis-assembly.