Warning alarm back working

[Robert Mann]

With much help from Ken Kloeber I have the warning alarms fully functioning.  It is a strange system, and I ended up replacing a good number of parts.  The original issue was a weedy sounding alarm sometimes, progressing to no alarm at all.
1)  the oil pressure switch had a loose terminal with an oil drip,  so I replaced with a NAPA OP6624SB,  2-7psi normally open switch. The original switch checked out good.
2) the plastic key switch fell apart, I replaced it with a Cole Hersee, brass unit M-550- NO from Defender
3) once i was sure these parts would hold up I finally figured out there was actually 2 problems.  The buzzer itself was bad, checked by testing across the battery. It was replaced with the original part Z4180 from Catalina direct.  Also, the ground at the glowplug solenoid was poor.  I removed the ground connectors and cleaned the bracket really well with emery cloth and put the grounds together on the same side of the bolt.

Once the above was done, there was battery voltage 14.2 volts at both sides of the buzzer when the engine is running with oil pressure.  When the engine was stopped with zero pressure, there was battery voltage on the buzzer +ve terminal and 8.4 volts at the buzzer P terminal (pulsing alarm terminal) with the alarm screaming.  Previously I had battery voltage at both sides of the buzzer when the engine was stopped, hence no alarm. 

I had checked the resistor and it checked with 997 ohms.  After everything was working I soldered a new resistor pigtail and a spare.  I did this because I wanted to be sure nothing was corroded.  I got the resistors (1000 ohms 1/2 watt) from Amazon $6 for 100 pieces!!! I didn't replace the 10A breaker as it checked good.

The system now wakes the dead. 

As mentioned Ken's help was massive, I believe we figured out how this circuit works, with voltage flowing in different directions, depending on the oil pressure switch status, open or closed.  The way the wiring is run and the connection points makes for a load of potential failure points.

All of the above not withstanding, I think Ron's solution of ripping it all out and wiring a normally closed oil pressure switch into the system makes for the most reliable system.

[Ron Hill]

Guys : I like Roberts' last sentence about ripping it all out and rewiring!!

The whole idea behind that complex M35 & M35BC engine wiring is so if the engine has no oil pressure it will quit (from fuel starvation) because the electric fuel pump will shut off.
Great idea, but in the C34 with the higher fuel tank, the engine will keep on running because the fuel will gravity feed thru the shut off fuel pump!!

Rewiring is simple, cheap, easy to do and results in a more reliable system!!!   

A few thoughts