2000 silverado trailer wiring harness ???

[truckeez]

hi Im trying to figure whats uo with the new to me 2000 silverado, I love the truck, and now trying to get some work done--hauling a stripped car to the scales to pay for title transfer. I fould the fuse box under the hood-- No way to rigg a trailer light harness to it-- ansd apparantly no hot take off points under the dash-- except maybe the cigarette lighter.

The rear of the truck has a dummy plug in the rear bumper-- but no wires going to it, i looked around and found a whacked off harness with the Wire ends all sealed over with plastic???

Is this one of the GM scamms to force an owner to take the truck in to have a tech install a plug recepticle - since they know which wires go where, or am I missing something? since its a 4.3 it's very possible it was never used to pull a trailer before.
Any insight would be appreciated Thanks--Truckeez.