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Oil pressure sending unit swap...BUT What to do with wire #2

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Dave448

Probationary Member
9
0
Jun 22, 2012
ft laud, Florida
My 95 420a eclipse has a 2 wire oil press sender PS277 $45 special order.....and I'd like to use the 96 up 1 wire version PS278 $15 available locally....but what does the 2nd wire do on mine?

Started out replacing timing set, fix oil leaks, mounts...HEY my whole motors apart...how did that happen?! LOL! Accidentally BROKE the oil pressure sw while hoisting the block out. Oops! Now $600 later give or take...heres more unplanned $. If I can swap to the 96 up type I can save money and waiting time. Sooo anyone know what mystery wire # 2 does?

The FSM diagram (below) shows 1 wire and 2 wire oil press sender plugs BUT does NOT show individual wires on the diagram. It appears the light gets 12v from the ign switch and the ground is applied via the oil press switch till the car starts then ground is removed to turn the light off.

1. Does wire #2 go to the ECM to shut off fuel pump if pressure drops? Ive seen other posts that say there is no such functionality.... (but that info may be incorrect) ...so...maybe or maybe not.....

2. Does the 2 wire switch pass signal from wire 1 to wire 2 and ground at another location? Its broken open and appears to ground directly to the block inside the switch...so....again...maybe or maybe not....

3. Does wire 2 maybe go to the Confusselator valve? Hmmmmm....!! :p

I considered (and dismissed) the idea of an aftermarket gauge bcus its just a daily driver...not a tuner and a gauge would be out of place.)

If anyone knows what mystery wire #2 does might save me another $30 or so unplanned $$$ and even more down time waiting for the part. BTW if I can pull this off i know i'll need to hit the boneyard for a suitable plug for the 96 up sender switch but they usually have lots of eclipses (usually with all the good stuff gone already).


Thanks in advance.
(NEWB) Dave

FSM diagram for all the good it does....
 

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The oil pressure switch has only 1 wire. The other switches connector (one with circle and 3 horizontal lines under it) is a device ground (through switches casing). Connector A-07 is a 2 pin connector but the other pin is most likely unused on your model (it may even have a wire there that isn't used on your model).
 
Thanks for the reply.

I was thinking maybe 1 wire was unused...but then why did they go to the trouble of using a 2 pin oil sending unit and 2 wire plug in the first place? Here is a topic from forum " X " that shows the differences in the 2 sending units. The poster had a 96 non turbo and said autozone gave him the wrong part PS277 which is exactly the part my 95 non turbo has so it definitely changed in 96 to the 1 pin model PS278 ( which is what I'm hoping to convert to. )

2pin PS277 (1995) and 1 pin PS278 (96 up) visual comparison
http://www.dsmtuners.com/forums/420...0a-oil-pressure-switch-broken-block-help.html

I tried to backtrace the wires today at the sending unit plug.

1. I tested with the probes in both connection holes of the plug and got nothing.
2. I tested each wire to ground and got nothing.
3. With the key on I tried testing each wire to the positve batt terminal and got nothing. Since the 12v oil light should be powered thru the ign switch (per the FSM wiring diagram) I was anticipating i'd be able to read continuity from one of the wires in the oil sender plug thru the bulb filament and to the 12v batt terminal but i got nothing. Im wondering if theres a relay that turns on when the battery is connected and the key is to ign 1 that sends power to everything or at least the dash circuit? If so thats why i wasnt reading thru the oil light bulb bcus theres no battery in the car.

I get what you said that they may not have used 1 wire...and its possible...but at the moment i've got no continuity from either wire to 12v and test #3 shudv yielded continuity thru the bulb filament unless gauges and idiot light power is supplied thru a relay (or the ecu and I dont know why they would do that.)

What happened to service manuals that show every wire and every color? This block diagram stuff is for the birds....

Further back tracing may have to wait until its all back together and i re-install the battery....unless you (or someone else) has another suggestion....
 
You have some good points and have done good research. I'm looking at 97-99 FSM (you too?) because I don't have every single year. Sounds like Brandon in post 4 of your link is right ("some sensors on the 95 are different from 96+ cars"). You'll have to look at a 95 FSM to see what the wiring is. Some libraries have the Mitchells or Alldata auto manuals for every year that you can look at for free which you might try.

I seriously doubt there's a relay in the oil light circuit but then this is Chysler and they are famous for having something old fashion or goofy - they often do. Although I doubt even they would have a relay. Have you checked the bulb itself and the fuse for that circuit?

I recommend examining the 95 diagrams before going to the 96 sensor. Perhaps the other wire is significant or you'd have to change it somehow if you want to use the 96 sensor.
 
No I havent checked fuse or bulb but theres no reason for either to be bad. Everything was working...warning lights gauges etc.... b4 I started dis-assembling the motor and theres been no power applied since bcus its still apart.

BELOW I posted the same diagram I did earlier EXCEPT this time I included the top part that got cut off and added the circuit trace I tried to prove out. It shows the oil light connects directly to ign1 and only a fuse in the circuit...no relay and no ecu indicated along the way. The blue trace I added shows the oil light circuit path and should have continuity from + batt terminal (which connects to ign1 with the key ON) and at least one of the 1 wires in plug A-7 (should be the Y yellow wire) but I got nothing on the meter tho. Maybe that other wire does go to the confuzzelator valve bcus its got me confuzzled!

BTW my svc manual is a CD Compilation I got years ago and covers 90-99 eclipse so it may be lacking in some areas. I THOUGHT it was official mitsu manual but....? I hate PDF manuals anyway! Nothin like the real thing! Im sure a REAL 95 manual ON PAPER wud narrow it down. I'll check the library but theyre sorely lacking in technical books available online. Maybe someone will read this post and come up with a better diagram.
 

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  • Eclipse oil pressure sending unit circut schematic w my blue test trace.jpg
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BTW my svc manual is a CD Compilation I got years ago and covers 90-99 eclipse so it may be lacking in some areas. I THOUGHT it was official mitsu manual but....? I hate PDF manuals anyway! Nothin like the real thing! Im sure a REAL 95 manual ON PAPER wud narrow it down. I'll check the library but theyre sorely lacking in technical books available online. Maybe someone will read this post and come up with a better diagram.
Yours looks like the one most of us have, the DSM Backup Manual CD. It is a copy of the official mitsu manual but they couldn't supply every 2g year so for the electrical they choose the 1997 manual.
Call a larger library first and ask if they have Alldata or Mitchells auto manuals. Our county library has both.
 
Ok I went to the library and got this wire diagram of the 95NT for ya. The other yellow-red wire on pin 2 as you can see is the sender for the stock oil pressure gauge. The 95 turbo and all 96-99 have the two on separate plugs.
 

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  • oil pressure switch & gauge sender - 95 Talon NT (from Mitchells).jpg
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Dude thats so cool you got the diagram for me! You rock! :hellyeah:
I'm still working on it. Re-assembling the engine. I went to a local library here and all they had was the Hardcover Chiltons manual for 95-99 import cars and the smaller paperback for 90-98 Eclipses. No Alldata or Mitchells in the county library system. Those chiltons manuals are pretty much useless for electrical. 1 has minimal electrical diagrams and the other has engine wiring only and shows the generic block diagram for the oil sender.

After seeing your diagram here it makes sense now! 95 was a dual switch/gauge sending unit which is probably why it's so expensive. Mitsu likely changed that setup because if that single sending unit went out you'd lose all your oil pressure indicators. 96 up seperated it to a 1 wire oil light switch and a separate oil gauge sending unit. Ahhhh clarity at last....

I went to the boneyard a couple days ago and dragged my 100+lb toolchest (never know what you'll find so go prepared) around in 92deg heat for hours! Came across a few Eclipses...most of the good stuff gone as usual. Was hoping for an early 95 2 wire oil switch to test with a meter for continuity but the oldest I found was a late 95 which had already gone to the 1 wire unit. I cut the pigtail off so I can go to the 96 up switch...and now THANKS TO YOU....I know I can use it and don't need that yellow/red wire! :thumb: Already called on the new switch and its being held for me at the parts store.

Hmm....This all still leaves one issue though. With both wires accounted for...that leaves no wires to hook up to the CONFUSSELATOR VALVE. ROFL

Thanks again for thinkin about me. I really appreciate it!

Have a great weekend!
Dave
 
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