Ducati Monster Forum

I've recently picked up a 2006 Monster 620. Thanks to the information I found on this site I was able to diagnose the fault in the fuel pump wiring and was able to clean the inside of the flange plug, re-solder the connections, and get the bike running. All was well until last weekend's washing. After the wash the oil pressure light stays on. Here's what I have done since then:
1. Unplugged the wire at the sensor to check for water leakage: no. Blew it out with compressed air anyway: still no. Cleaned the connectins with WD40, dried them, tried again: still, the light stays on when the engine is running.
2. Tested the wiring from the switch connection to the insruments by grounding the wire for the oil pressure switch. Grounded, the light is on. Ungrounded, the light is off. So the light works as it should.
3. Check the switch. Attached a test lamp between the switch and battery. The test lamp is on with the engine off. The light goes out when the engine runs. Lamp lights again when the engine stops. So, the switch checks out.
4. Plug the wire to panel back in. Engine off: light on. Engine running: light on. Engine stopped: light on.
5. Back to the test lamp. Engine off: lamp on. Engine running: lamp off. Engine stopped: lamp on.
6. Grabbed the multimeter and set it to test continuity. Attached to switch and a cylinder fin. Engine off: continuity tone sounds. Engine running: continuity tone is silent. Stop engine: continuity tone sounds again.
7. Switched to ohm meter mode: Engine stopped: resistance of a few ohms. Engine running: Open Line. Engine stopped: a few ohms again.
8. Switched to k-ohms. Engine stopped: reading near zero. Engine running: about 2k ohms (?). Engine stopped: near zero resistance.
9. Went back to auto-ranging: Engine stopped: a few ohms. Engine running: Open Line. Engine stopped: a few ohms.
10. Plugged the panel lamp back in: Stays on when the engine is running.
11. Attached the test lamp: Shuts off when the engine is running.

I'm stumped. I don't have a spare switch laying around that will fit.

The connection got wet when you washed it, once it dries out it should go back to normal function

You get to know your bike. That's good.

Very common fault on our bikes.

It sat unplugged since last Saturday. I'm in Arizona. It HAS to be dry by now. Is there someplace for water to become really trapped and resist drying even in 100F plus temperatures? I have thought about just running it (since the test lamp indicates all's OK) and allowing engine heat to really soak the switch.

One of your tests confirms pressure, doesn't it?

Those connectors are really good at letting water in and keeping it there.  You proved the sending unit is functioning as well as the light.  The problem is in the connection.  Could be still damp,  corroded or loose.  When you finally get it working, pack the  connector with dielectric grease.  Also make sure the connector from the stator ( three large yellow wires) is in good shape and pack with dielectric grease.

A friend had an oil pressure gauge with the correct fitting adapter so I ran a mechanical test. Plenty of oil pressure. Maybe too high (50 psi at idle) but I have not yet changed the filter or cleaned the screen. Rode for about an hour today and the light is still on so the switch is clearly faulty. It's over 110 here in the afternoon so if there was any moisture in the switch it must have had opportuinty to dry out after running at those temperatures. At least the switch will be quite easy to replace.

Thanks for the advice.

Cold engine:

1100-1300 rpm: at least 2.5 bar, 3500-4000 rpm: between 4 and 6 bar.


Hot engine (140°C):

1100-1300 rpm: at least 1. 1 bar, 3500-4000 rpm: between 4 and 6 Bar.

It's a long way to the top of the vertical cylinder.

Thanks for the numbers. In a cold (90F engine) the pressures were about 3.5 bar at idle and 6 bar at 3500 or so.

Today's ride to work confirmed that the pressure switch was in its last throes of life. It worked at the start at home. Was completely dead when I left work. Even after sitting for a few hours the switch is still open. I imagine that the diaphragm fractured.