Assuming that the 4000 has a control board you need to find out which circuit connects to the oil pressure sending switch. Many of these units used the oil pressure circuit as the shut down. No oil pressure meant shut down. I believe all they did was ground the oil pressure switch line.
Brian, Loretta & Daisy (Golden Retriever)
2008 HR Endeavor 40 PDQ , ISL 400
2010 Dodge Ram 1500 Toad