Newbie and Reverse Indicator light

Hi! Happy to have found this forum and have lurked for some time. I’ve found the info to be very helpful.
I’ve just bought 2005 Honda Rancher TRX350T and have been working on it for 2 weeks. I just took it on it’s maiden voyage deer hunting with a friend. It ran perfectly, though I’m still working out minor details.

I replaced all the burned out light bulbs, replaced clips missing, repaired the accessory plug, adjusted and cleaned the breaks, swapped out filters and fluids, and removed/repainted the heavily rusted racks. Looks much better!
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I need to research what kind of tires to eventually buy, and find a nice and simple gun rack for the front.

My biggest headache has been the reverse indicator light. The reverse indicator light on the panel isn’t lighting up, though the other 2 lights (neutral and the one at startup) do light up when turned on. It shifts fine with no issues and goes into forward and reverse. I swapped out the light bulb in the panel, but no luck. I checked the continuity from the bulb socket to the reverse actuator wire and it gave a good signal.
I haven’t been able to track the black wire yet, but thought maybe someone could point me in the right direction.

Thanks for all the info!