Fuel Pump, Oil pressure switch, and Ignition Circuit (2006 Mercruiser 5.0L TKS Alpha)

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csadams

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Jul 5, 2020
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Needing help finding issue with electrical circuit to the fuel pump. Problem came out of nowhere. Boat has been running good with no issues for most of the season so far. Yesterday started the boat in, while still warming up in the marina and the TKS choke engaged the motor just stopped. After some looking around found a 15 amp fuse in the helm was blown.

No power to the fuel pump when starting or after running. I have hot wired the fuel pump to make it run.

If I try to start the engine with the oil pressure switch plugged in the fuse blows again. Could this be as simple as a bad oil pressure switch? Could it short to ground if bad?

Please help as we have a big trip driving pulling the boat across country to lake Powell that I am trying to get prepared.
 
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csadams

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Jul 5, 2020
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Should the purple wire and purple/yellow wires go to ground when pos is disconnected from battery? think I have a short in the harness at this point. If anyone has some ideas it would be appreciated?
 
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csadams

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Jul 5, 2020
Messages
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Ok, Made some headway. Diode assembly is failed open. From what I can tell this is the cause of the grounding to the ignition circuit. Fuel pump now is running with the diode removed. Fuel pump runs both when cranking engine and while oil pressure tells it the engine is running. Now to determine if there is an issue with a wiring, the thermal switch itself, or the tks module solenoid. Still looking for insight. How can I test the TKS module or thermal switch?
 
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