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Oil Pressure Indicator Lamp

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WhitleyStu
Join Date: Mar 2006
Posts: 27 Northeast Indiana
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2007-11-20          148531


When changing the oil on my BX2230 I noticed the wire to the oil pressure sending unit was broken off the electrical connector that snaps on the tab of the sending unit. I crimped on a new connector and pushed it on the sending unit. I started the engine after the oil change and just for the heck of it I unplugged the connector to the sending unit. No indicator light lit up on the dash. If I am thinking right I should have had an oil pressure light come on. So, do I take the steering wheel and dash off and check the bulbs? Thanks for any advice...
Stu




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candoarms
Join Date: Mar 2007
Posts: 1932 North Dakota
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2007-11-20          148533


Stu,

I believe you're correct. When the wire is disconnected from the sending unit WHILE THE TRACTOR IS RUNNING, you should have an oil warning light appear on the dash.

However, this light should also appear when you first turn the key to warm the glow plugs, prior to starting the engine. If the oil pressure warning light appears when you turn the key, the bulb IS NOT burned out.

I'm guessing that you have no oil pressure warning light when you attempt to start the engine. If this is the case, the bulb is likely the culprit.

Joel ....


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WhitleyStu
Join Date: Mar 2006
Posts: 27 Northeast Indiana
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2007-11-20          148536


I checked the manual to make sure which warning light on the dash panel is the oil pressure. I turned the key to the preheat position (engine off) and I do have a good oil pressure light bulb, but when I unhook the wire the light goes out. When the engine is running and I pull the wire off of the sending unit I get no warning light on the dash. Any ideas??? This is one indicator light I want to know is working properly... ....


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candoarms
Join Date: Mar 2007
Posts: 1932 North Dakota
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2007-11-21          148539


Stu,

I believe I know what's going on here, but I could be wrong.

Provided that you have only one wire going to the pressure switch, it's possible that the switch will only allow a completed circuit when the oil pressure is low.

In other words, I believe you have a hot wire going to the lamp. On the other side of the lamp, you have a ground wire that goes through the oil pressure sending unit. When the oil pressure drops, the switch makes contact, and the path to ground is subsequently completed, which allows the lamp to light.

You can test this theory easily enough by placing an ohm meter on the sending unit. With the tractor off, your sending unit switch should be closed. (low oil pressure condition) By touching one lead of your ohm meter to the sending unit's terminal, and the other to the tractor frame, you should read close to zero ohms, indicating a closed circuit......which would allow the lamp to light.

When you start the engine, the ohm meter should show an open circuit, or very high resistance. (high oil pressure condition)

Be sure to zero your meter before attempting this test. Touch the two leads of your meter together to see if the meter reads zero. If you have a digital meter, you won't have to adjust for zero, but this test will let you know whether or not your meter is working properly prior to using it.

If you read very high ohms (high resistance) while the tractor is running, this means that the switch is open, preventing the lamp from lighting......as should be the case.

The problem with this design -- if this is indeed the case --- is that in the event the wire came loose, or was removed by a twig, etc. -- you wouldn't know if you lost oil pressure until the next time you go to start the engine. The warning lamp won't light when you place the switch in the preheat position.

Joel ....


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bloggins
Join Date: Apr 2006
Posts: 104 Kingston, Ontario
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2007-11-21          148543


Condoarms is correct. The pressure unit creates the ground to light the lamp. Engine running = no light, pull wire still no light = because no ground available to light the bulb unless the oil pressure drops to zero closing the contacts in the sender unit. ....


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candoarms
Join Date: Mar 2007
Posts: 1932 North Dakota
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2007-11-21          148544


Bloggins,

I'm from the old school of thought that taught me never to place a switch in the ground side of any device.

It goes against everything I've been taught, when I see a switch in any ground wire.

I believe the hot wire going to the lamp should be switched by the sending unit, and the ground wire from the lamp should be permanently grounded to the tractor's frame.

It's very difficult to troubleshoot any electrical system when both sides of the circuit have to be checked. Dammit....ground is supposed to be ground. Ground isn't supposed to be broken ANYWHERE! Only the hot side of a circuit is to supposed to be switched.

The sending unit should have two terminals on it. The hot wire should go to the sending unit. The switch should be open when the oil pressure is high. The ground wire should come off the neutral side of the lamp socket........but that's the old-fashioned way of doing things, I guess.

Joel ....


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WhitleyStu
Join Date: Mar 2006
Posts: 27 Northeast Indiana
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2007-11-21          148547


I was not thinking about the ground being on the "other" side and with your example I understand what is going on. At least now I know I have a reliable oil pressure warning light. Many thanks to you gents for your help...
Stu ....


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mobilus
Join Date: Jul 2007
Posts: 171 Clay County, TX
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2007-11-21          148574


Here's a link to a simple diagram that might help. When the oil pressure is within established parameters, the plunger is forced in, bridging the contacts' gap. ....


Link:   

Click Here


 

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