Tough question. Some are sourced from the Alternator, some utilize a screw-in pickup mounted at the bell housing/flywheel area and some are sourced from the transmission's speed sensor through the MD3060 trans harness. I can't answer for you definitively but having the Oshkosh wiring diagram would certainly answer your question.. if you have or can find one.
94-Newmar Kountry Star 40-KSDP
Spartan/Cummins 8.3C-300HP/Allison 3060 WTEC-II/25yr RV Tech RVIA Certified/Onan-Cummins Certified