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Front and rear park light would work on a common out put from the switch, Front and rear marker lights are probably spliced in to those circuits.
What chassis is your coach built on , Chev? Ford?
Getting a chassis wiring diagram may help. At least you can get a wire color to trace it down the frame rail.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.