Jon, I have a 1977 coach with a Cummins '555' engine. As suggested by Mike Clarke above "The override switch on the Cummins '555' (the manual override switch) has to be held on (spring loaded position) in order for the engine to start. Once sufficient oil pressure was obtained, the oil pressure override switch can be released. If the engine loses oil pressure, this system will probably shut the engine down, except when the switch is held open".
However on my coach, the switch is in series with the high temperature safety as well. Either loss of oil pressure or high engine temperature will shut down the engine. The override will allow a brief start to pull off to a safe area.I had to use it several times on long summer hill climbs in Arizona when the old girl got too hot. A P/O had by-passed both safety switches but I have reconnected them, and rely on them doing their job to protect the engine. You may have to trace some wiring to see which configuration you have.
Enjoy.
|