Hello everyone, 

My fuel pump does not energize when I turn the key to the on position and push the glowplug button. I also get an intermittent low oil pressure buzzer when the key is in the on position. 

I've read the very long thread about the glowplug/low oil pressure/preheat solenoid/fuel pump circuit here: https://c34.org/bbs/index.php/topic,3347.0.html.

I understand that there are two sides to the fuel pump circuit: the low oil pressure sensor switch that only closes after the engine starts and oil pressure builds up; and the preheat solenoid that closes and energizes the glowplugs. The fuel pump only goes on when at least one side is closed. 

I replaced both the fuel pump and the low oil pressure switch. Neither solved the problem, though when I bypassed the low oil pressure switch by disconnecting it and jumping a wire between the two connecting wires, the fuel pump energized, as you would expect. So that side of the circuit does seem to work when/if the oil pressure switch closes when the engine builds up enough oil pressure after starting. 

I put a multimeter across the preheat solenoid and got 12 volts on the incoming terminal with the key off, and 12 volts on the outgoing terminal with the key turned on and glowplug button pushed. I also tested the 10 amp circuit breaker on the solenoid and got around 8 volts, though I'm not sure if that's significant or not. To test the circuit breaker in another way, I bypassed it and wired the circuit directly to the small, starboard solenoid terminal, but the (new) fuel pump still did not energize. 

At the same time, I tested the first glowplug in the line on the engine with my multimeter and got 0 volts with the key on and the glowplug button pushed. That's when I also noticed that I get no voltage drop on my voltmeter at the engine panel when the key is turned on and the glowplug button is pushed. I also shot my digital thermometer on their heads, and there's no change with the glowplug button engaged. So the glowplugs aren't getting power.

From all this testing, I've concluded that the oil pressure switch side of the circuit is fine, but that on the solenoid side, no energy is going to the glowplugs (even though the solenoid appears to test fine) and this is somehow also preventing the fuel pump from energizing. 

I've read about the resistor assembly (westerbeke part 039806) that's built into one of the wires leaving the solenoid going to the glowplugs, and plan to replace that next to see if it addresses the issue. But I have a few other questions:

1. The engine actually starts fine, even though the fuel pump and glowplugs apparently aren't getting energized. I understand that gravity can feed fuel to the engine with the tank at least half full, but can the engine actually start without energy to the glowplugs?
2. What is the purpose of the 10 amp circuit breaker on the solenoid? Is it necessary or can I eliminate it?
3. Is a bad buzzer at the panel a possible cause, somehow shorting the solenoid side of the circuit?
4. Is it possible that my glowplugs are burnt out? Would they show 0 volts if burnt out, or should they still be getting energized?
5. Any other thoughts on what else I can test?

Thanks in advance for your thoughts. Cheers, Joe

Joe Bousquin, San Francisco Bay
Sausalito Yacht Harbor
SV "Sylbo"
1994 Catalina 36 Mk 1.5, hull number 1337
M35AC engine