for starters, directions are always as viewed from the driving position, left is the driver side .... Chev wiring diagram [as seen on screen you're looking from the front of the vehicle] shows 3 wires on one post of the ammeter [used as a junction point] and 2 on the other, if your original harness had spliced wires away from those terminals, ignore that, is not a good setup even if original and could as well have been changed sometime .... the wire you think is missing would be power to the lights, examine if the new harness might be supplying it from somewhere else, if not you can add the indicated short wire from the ammeter to the switch [maybe some extra single wires in the harness kit?]

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature we find it attached to the rest of the world" John Muir
"When we tug a single thing on an old truck, we find it falls off" me
Some TF series details & TF heater pics & Rust-a-holics Unanimous parking lot