Oil Pressure Sensor Or Switch?

PharmD

PharmD

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Hey guys. I didn't really want to hijack this old thread, but I’m having the same issue that's in there.
I have a 1998 Chaparral 2130 SS with a Mercruiser 5.7L Thunderbolt.
I ground the gear lube box and it works. I ground the temp sensor and it works (alarm doesn’t stop after I do this one, but I am assuming that’s normal because I opened the circuit). I’m trying to troubleshoot the oil pressure sensor but I’m not certain I am looking at the correct part. I can’t find this part anywhere online. I’ve attached the picture of it. It has 2 wires, a purple (hot) and a purple wire with a yellow stripe. Is this the oil pressure switch, if not, what exactly is it? I don’t really see anything that looks like your typical oil pressure switch. Thanks a ton for your help and advice. I greatly appreciate you. IMG_0590.jpeg
 

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Mc Tool

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That sure does look like a oil pressure switch , and that its next to the filter ..... might be .
 
PharmD

PharmD

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04fxdwgi25 said:
If you have the engine serial #, go here:

Unit with the purple and purple/yellow is the switch that cuts off the fuel pump if the oil pressure drops. Basically a safety switch. Item 5
View attachment 405813
View attachment 405814
The oil pressure has lt blue wire. Probably the rusted fitting round can like thing below the one you were looking at.

View attachment 405815
Click to expand...
@04fxdwgi25 Thanks a bunch. This is what I found. Will I need to buy both of these parts, or just the one that says “switch oil pressure sensor”? That actual part I think is obsolete, so the superseded part will require some basic wiring to get it plugged in. However, I will say that grounding that wire with the yellow stripe doesn’t set the alarm off. Is it supposed to? Thanks again.
 

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Last edited:
alldodge

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Need your serial number.
Not all but most EFI/MPI motors does not have a direct oil pressure switch to alarm. The oil pressure switch sends signal to the ECM and the ECM is what sounds the alarm. Grounding the switch will not sound the alarm on it's own
 
D

dubs283

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Based on the pics im guessing OP has a carbureted engine, not efi. Pics posted #1 show the oil pressure sender (for the guage) and oil pressure switch (for the fuel pump)

Neither of the components pictured in post #1 have any correlation to the audio warning system.

OEM for a carbureted, thunderbolt ignition engine of OP's vintage equipped with an audio warning system would have the oil pressure switch for the warning system installed at the aft end of the intake valley in the block adjacent to the distributor. The associated wire color for the audio warning system is tan/blue (oem)

Sounds like OP has verified the horn works by grounding the tan/blu associated with low gear oil and temp. Key on/engine off should activate the audio warning horn due to no oil pressure. Test would be to ground the tan/blu for the oil pressure switch and listen for horn (with key on/engine not running), if no horn that portion of the circuit is faulty. If yes horn most likely culprit is the oil pressure switch.

Absolutely not out of the question for the switch to have failed
 
PharmD

PharmD

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alldodge said:
Need your serial number.
Not all but most EFI/MPI motors does not have a direct oil pressure switch to alarm. The oil pressure switch sends signal to the ECM and the ECM is what sounds the alarm. Grounding the switch will not sound the alarm on it's own
Click to expand...
@alldodge SN# 0L056178
 
PharmD

PharmD

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dubs283 said:
Based on the pics im guessing OP has a carbureted engine, not efi. Pics posted #1 show the oil pressure sender (for the guage) and oil pressure switch (for the fuel pump)

Neither of the components pictured in post #1 have any correlation to the audio warning system.

OEM for a carbureted, thunderbolt ignition engine of OP's vintage equipped with an audio warning system would have the oil pressure switch for the warning system installed at the aft end of the intake valley in the block adjacent to the distributor. The associated wire color for the audio warning system is tan/blue (oem)

Sounds like OP has verified the horn works by grounding the tan/blu associated with low gear oil and temp. Key on/engine off should activate the audio warning horn due to no oil pressure. Test would be to ground the tan/blu for the oil pressure switch and listen for horn (with key on/engine not running), if no horn that portion of the circuit is faulty. If yes horn most likely culprit is the oil pressure switch.

Absolutely not out of the question for the switch to have failed
Click to expand...
What you are saying makes total sense to me. I was all but certain that I was looking for a tan/blue wire but never found it. I looked all around the ignition coil, but never the distributor. I just assumed that the switch and the sender were in the same proximity. This makes total sense. I will look again and try yo find the sensor. Thank you so much for your help.
 
Scott Danforth

Scott Danforth

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blue wire is connected to the bell looking pressure sender.

tan wire is connected to the temperature switch at the thermostat housing.
 
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