687 lawn mower oil pressure light

[GearHead27]

I am working on a john deere 687 front mount mower that I have recently put in a new engine in. I got the more set up and it runs put I noticed that the oil pressure light is on, and I have test it and have good oil pressure. Is there anyway to test the oil pressure sensor to see if it is bad or if it has a bad wiring connection

 

[KennyV]

WELCOME to LawnWorld.... from another Kansan.
If you know you have good oil pressure, check the sender and wire. With oil pressure it should measure an 'Open' to ground using the ohms setting on your meter. The sender is just a spring loaded switch, it completes the circuit path to ground. If the sender switch is an open to ground with oil pressure... then the problem will be the wire is shorted to ground somewhere along it;s path....
What part of Kansas are you?:smile:KennyV

 

[GearHead27]

Im from Lawrence I have replaced the sender and light still on and it is working properly do you know where that wire is suppose to connect to in the wiring circuit

 

[KennyV]

... do you know where that wire is suppose to connect to in the wiring circuit

It should go directly to the lamp, it supplies ground to turn that lite on. The key switch supplies the needed 12 volts to the other side of the lamp.
If you disconnect the wire at the sender is the lamp still lit? If so then the wire is shorting to the chassis or frame somewhere between the sender and the lamp.
BTW the sender switch on the engine should measure a Short with the engine Off, & No oil pressure...
And it should measure an Open with the engine Running & oil pressure.... :smile:KennyV

 

[itstorque]

Hi, new member here ... I know this is an old thread but I thought continuing it might be better for people coming along later with the same issue, as this thread did not come to a conclusion with a "solved" answer.

I have just repowered a Ford LS55 with a B&S Vanguard 23 HP from a Kohler Command 18 that gave up, and I have the exact situation the OP did.

If you disconnect the wire at the sender is the lamp still lit? If so then the wire is shorting to the chassis or frame somewhere between the sender and the lamp.

No, the light goes of.

BTW the sender switch on the engine should measure a Short with the engine Off, & No oil pressure...

Are you saying, with key on (voltage to light) and no engine running, there should be a light?
This is what I expect, but no, that is not what I have. Key on not running = no light. Engine running = light.

And it should measure an Open with the engine Running & oil pressure.... :smile:KennyV

Apparently it is open with no oil pressure (no ground to complete circuit to light)

I am wondering if this sender was designed to be used with "kill circuit" rather than a light.
Are there two types of oil pressure senders with opposite behavior?

Finally, how can I verify oil pressure without this sensor? The OP said he did. I am paranoid at this time that there may be no oil pressure in my brand new engine.

Thanks in advance.

Rich

 

[KennyV]

WELCOME to these Forums...
Rich you can get a low pressure gauge and plumb it into the port the sender is now threaded in... that will give you a constant read out, But a light is More apt to catch your attention... You are less likely to notice a needle on a gauge dropping off... :smile:KennyV

 

[KennyV]

As to the pressure switch... if it is working backwards, replace it with one that works at the pressure you want to be alerted at... all you need is the correct thread and select the pressure you want.
You could actually place a 't' fitting and use Both a pressure indicator light And a pressure gauge... :smile:KennyV

 

[itstorque]

Thanks Kenny ... the fact is that the light is nearly impossible to see "on" in normal daylight conditions, but if in the garage or at dusk it's detectable.
I think I'd rather have it wired as a kill mechanism if the oil pressure fails, as long as it was reliable. I have flat land. - Rich

 

[itstorque]

I just tested and can report the following:
Engine running, 0 ohm from pressure sensor to ground.
Engine not running, open from sensor to ground.

So I'm still lost.
The "idiot light" should not be on unless the pressure is NOT there. Maybe the original wiring used a relay or something to reverse the outcome. Not quite sure how that would be, I'm just grasping at straws I guess.

If I wire the sensor to the kill wire post, it grounds the coil when there IS pressure. Again, the opposite of what makes sense.

Any further ideas?

 

[KennyV]

On my big ZTR I have Murphy gauges on the oil pressure and engine temperature... either one will activate the diesel fuel shutoff solenoid... During operation they work great as it is not practical to 'see' the gauges during operation.

If you do set yours up to shut down with the loss of oil pressure, you will have to wire it up with a work around at start up when there is no oil pressure. Use relays set for a positive kill with any loss of pressure... You could use the sender switch you have wire the relay to have the energized relay contacts being normally Open to your kill, that way you can energize the same relay with your starter solenoid feed Plus a Diode, for start up.... :smile:KennyV