Jim, I don't want to argue with you, but in the interest of accurate information I will make this one last post.
See the partial schematic below with my colored markings.
The shutdown relay terminal 85 gets 12V from the engine circuit breaker. This is one side of the relay coil (my blue wire). The other side of the coil, terminal 86, goes to the oil pressure switch then the engine temp switch. If EITHER the temp switch or the oil pressure switch switches to ground the relay coil will be energized.
Now, when the coil is energized terminal 30 (common) is connected to terminal 87 (normally open). if the waste tank is not full then terminal 30 has 12V on it (my red wire from the breaker through the float switch to the relay terminal 30). This means terminal 87 will become hot. As you can see terminal 87 is connected to the check engine light.
With the relay thus energized, terminal 87A (normally closed) is not hot. If you follow 87A out it goes to the fuel pump and engine coil pack. It's the one that has to be hot for the unit to run but under this scenario it's cold.
So, if the high temp switch completes the circuit to ground, energizing the relay, the result is a check engine light illuminated and the wire to the fuel pump and coil pack is dead. This is exactly opposite from what Keith describes any way you look at it.
Further, look at the way the temp switch and oil pressure switch is wired together. Note that either one can ground pin 30. So, if what you say is true, and the temp switch grounds the circuit to run the unit then look closely - if the oil pressure switch grounds then the circuit will be grounded no matter what the temp switch does. If there is enough oil pressure then the temp switch would not be able to shut the unit down, and vice-versa - if the temp switch is made then the circuit is grounded and the oil pressure switch would not work if there was a loss of pressure.
Any way you look at it, the schematic is drawn such that if either the temp switch OR the oil pressure switch makes the relay will be energized, lighting the check engine light and shutting down the unit.
Now, if someone had accidentally switched the wires between 87 and 87A the unit would work as you described. The wire to the temperature switch would have to be grounded for the unit to run - BUT - that means the oil pressure switch would no longer function.
A quick test for Keith to do (and he should) would be to pull the wire off the oil pressure switch and see if the engine stops, leaving the through-connection to the temp switch intact. If it doesn't stop that way, he should try jumpering it to ground. One or the other should kill the engine.
If the oil pressure switch does kill the engine with the temp switch connection grounded as Keith has it now then it just means the actual wiring does not match the schematic.
If the oil pressure switch has no effect then there is something miswired on the unit (as I suspect).
I normally would just let this go, but there is a good chance Keith's oil pressure switch may not be working and could cause him big trouble if there is a loss of pressure and it fails to work as it should.
Jim, I know you can read the schematic and it just doesn't match with grounding the temp switch to make the unit run.
End of rant....
