Farm Equipment - AC7040 Oil pressure switch

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AC7040 Oil pressure switch

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Category: Allis Chalmers
Forum Name: Farm Equipment
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URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=195106
Printed Date: 09 Feb 2025 at 7:53pm
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Topic: AC7040 Oil pressure switch

Posted By: jazzsuds
Subject: AC7040 Oil pressure switch
Date Posted: 12 May 2023 at 11:49am

I just installed a new set of guages on my 7040 and when I connected the oil hose from the guage to the oil pressure switch I noticed there is a electrical connection at the back of the switch that is missing the wire. Does anybody know where that wire should go to and what size guage it should be?

Thanks folks.

Replies:

Posted By: MACK
Date Posted: 12 May 2023 at 8:49pm

Engine oil pressure sender should only have one wire. MACK

Posted By: jazzsuds
Date Posted: 12 May 2023 at 10:11pm

yes but where does it go to?

Posted By: Codger
Date Posted: 13 May 2023 at 5:36am

Right to the gauge. The oil pressure "sender" is a varistor meaning a variable resistor and the ground side of your pressure gauge connects to this terminal. On your gauge there should be two, or three wires to connect. One is a light, (if present) the other a 12VDC that is active, (hot) with the ignition key on, and this third connection for the "sender" to connect to.

The part referred to as "sender" is actually/technically a "transducer" which means a device that changes pressure to a variable voltage output that varies by the amount of resistance in the monitored system. This resistance changes as input pressure changes and in this scenario, you see as gauge movement; less pressure, less gauge deflection, more pressure, more gauge deflection.

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That's All Folks!

Posted By: DrAllis
Date Posted: 13 May 2023 at 6:40am

A model 7040 tractor never had an oil pressure gauge from the factory. They had a red idiot light in the instrument panel, so the sender for this red lite is behind the oil filters and is a one-wire push on spade type sender.

Posted By: Codger
Date Posted: 13 May 2023 at 10:52am

Never seen a 7040 myself but assumed you replaced an original gauge. The "sender" referenced is a simple on/off switch calibrated for a certain pressure to trigger an indicator commonly referred to as an "Idiot" light.

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That's All Folks!

Posted By: jazzsuds
Date Posted: 13 May 2023 at 1:07pm

Thank you