Oil Pressure Sender/Switch Question???

Oil Pressure Sender/Switch Question???

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1979 CJ-7 with a fiberglass body and 1982 wide track axles, 258 I-6 with a 1995 4.0 head, HEI distributor, Motorcraft 2100 Carb, T-18 wide ratio tranny, Super Lift Springs and 33s, a 1997 BMW 328i, and a 2010 REDLINE CONQUEST TEAM Cyclocross Bike. :)
My Jeep will be titled as a 1979, but it has parts from many different jeeps.

I'm having a little trouble figuring out which oil switch I should buy for the CJ7 . Most 1976-1986 CJ7 's I've seen have the 2" gauge on the right, just above the stereo cutout . I'm finding all kinds of part numbers and prices for the sending unit however. I have no idea what year my wiring harness, or 2" gauge came from. The engine is a 1978 AMC 258 i6 / 4.2l . Do all oil sending units operate on the same ohms? Do some of them have only a one wire hookup while others have two?

Quadratec has one listed for all CJ years between 76-86 for $19 and another one for over $30. Advance Auto wants $36 for the oil switch for a 1979 and they only want $12 for a 1980.

Should I just buy the cheapest sender for whatever model year and change the plug if neccessary, or do they have different ohms?
 
Unfortunately, there are differences.

Without knowing what gauge you have, it'll be hard to match up a sending unit ahead of time. You could simulate a sender by finding a couple of resistors at Radio Shack (if they still sell resistors). Go with 10, 80 and 100 ohm. Maybe more but those at least. Wire them up one at a time and see how the gauge reacts. That should tell you what sending unit you need.

It may be easier to just get an aftermarket gauge that comes with a sending unit. You can use the existing wiring to run it.

Or you can get a mechanical gauge.
 
Unfortunately, there are differences.

Without knowing what gauge you have, it'll be hard to match up a sending unit ahead of time. You could simulate a sender by finding a couple of resistors at Radio Shack (if they still sell resistors). Go with 10, 80 and 100 ohm. Maybe more but those at least. Wire them up one at a time and see how the gauge reacts. That should tell you what sending unit you need.

It may be easier to just get an aftermarket gauge that comes with a sending unit. You can use the existing wiring to run it.

Or you can get a mechanical gauge.

I'm continuing to research this. I've found countless sites that offer sending units that are supposed to fit 76 through 86. If they offer a universal sender for that whole year range then the ohms have to be close enough between all the factory gauges for it to work. The gauge I'm using is just the stock plain old 2" gauge that looks the same in all years of CJ's I've seen.

I also found the info from the following link on a couple sites. It gives the ohm readings for a Jeep CJ sending unit without differentiating between years. That all leads me to think the ohms are pretty much the same for all of them.

Troubleshooting Jeep CJ Gauges and Senders

I'm starting to think the only difference is whether the wire connects to a tab on the sender or a bolt. I think I'll just buy whatever year one wire sender that's cheapest and change the connector if neccessary.
 
I also have a 1979 CJ with the same problem. what i discovered is there was an 80psi gauge that ran in what appears to be 79 only, all the rest seem to be 100psi gauges. im from the auto industry and i would guess that in 79 some one got a better deal on the 80psi gauges. then there was a supply problem and they went back to the 100psi gauge (more expensive but better supply). So now you and i are stuck buying the more expensive sender. all this being said any sender should work all it should affect is the accuracy of the gauge. there is a math calculation that will tell you how much. not enough to say so. i just want to know i have pressure and it is always about the same :)
 
I had this problem with my J-10 . I replaced the sending unit with what I , and everybody else thought it should be and it read 1/2 of actual. Not the end of the world , just not my first choice. when the
cj got new gauges, it was mechanical ,hands down, no question.:cool: Just make sure the hose is protected where it comes thru the fire wall it is full of hot oil at rather high pressure and will make a major mess or dump all your oil on the road in a very short time.:D
 

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