Yanmar 3GM30F Alarm problem

[smurphny]

Oil pressure alarm/light are coming on, key off, as soon as battery switch is turned on. Normally, the battery switch is on either "one" or "both" but alarm does not come on until key is turned on. The signal appears to be coming from the oil switch because when detached, alarm shuts off. Have checked panel connections for corrosion and they are clean. When the engine is started, all lights and alarms go off as usual. With the key in the off position, there should be no current running to the oil switch. Another hint is that the alarm signal and the oil light do not seem as loud/bright as normal when this is happening. Has anyone else experienced anything like this?

[smurphny]

Have found some info. on this problem on-line. Best guess is sending unit malfunction since it is apparently grounded (closed) when it should be open. Have ordered new one.

[DotDun]

The oil pressure switch will be ground when the engine is off, it's job is to close when there is no oil pressure. Looking at the wiring diagram, I wonder if your key switch is bad. Does the push button start switch work with the key off?

[smurphny]

I think you may be right, DotDun. Isolating the key switch will be the next logical step. For $14, replacing the oil switch is cheap and easy and it seems a couple of other people have solved the same problem by doing this (although it really makes no obvious sense). There should be, one would think, no current at all to the load side of the circuit with the key off. Could it be that the alarm is triggered by incorrect resistance in the wire, created by a bad switch? Seems unlikely as this old panel has no computer chips to "remember" anything. Before digging deeper and pulling things apart, will try replacing the switch. As always, according to Murphy's Law, the bad part will always be the last thing you replace.Thanks for your input, will update when I figure it out.

[DotDun]

The only other thing (after the key switch) that I can see it could be is something funky going on in the alternator that is putting + out to the charge lamp which gets back feed thru the bulb to the other lamps and buzzer.

Let us know what you find.

[smurphny]

You were right DotDun. Went over today and replaced oil sender with no effect as expected. Then swapped out the alternator with a spare. Problem fixed. Now to see if I can find a replacement rectifier/diode unit so I can to repair the original one. Spare is only 35A. Weird that the alarm turned off and the unit apparently charging when the motor was turning but then triggered the 30a starter circuit with 5-8 volts when stopped. Also, the indicator light which did not come on before when key was turned to "on" (thought it was just a bad bulb) lights up now and goes off when engine is started.

[DotDun]

I'm glad you found it!

[smurphny]

Thanks for the input DotDun. Will buy you a beer when I'm down Fl. way! Hope this post helps anyone else with the same problem as there seems to be no info. anywhere else and NOTHING in either the official shop manual or the other (name escapes me) engine manual I have onboard. One would think this would be included in any "troubleshooting" section: Alarm does not shut off when ignition key turned off----Faulty alternator----Repair or replace.

[DotDun]

Yeah, unfortunately, a lot of manufacturers don't live up to the term, 'Service Manual'. I recently struggled with a Yamaha F115 fuel injection problem on our runabout, it seems the official Yamaha service manual that I paid big bucks for is simply a 'how to tear it apart' manual, and not a very good one at that. Thanks to Internet forums, I read where others had the same problem and found my solution.

I'll buy us the second beer!! (I can never drink just one!)