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By rovison - 14 Years Ago
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I installed a new oil pressure sending unit on a 56 Merc. with a 292 cu. in. ( not a 312). I can't get it to read the oil pressure in the engine. I connected a mechanical gage and it records good pressure (65 to 70psi) The sending unit I used has a dual post on top of it and I only have one wire running from my gage. When I ground the wire with the key on the gage goes all the way to max. So its getting voltage. I don't know why they put a dual post on top of the sending unit or why my gage wouldn't register any pressure. Does anybody know what I could check out? thanks, Tom
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By YellowWing - 14 Years Ago
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Tom, your two post sender may be one terminal for ground and the other for the sender (sometime used to eliminate grounding problems through the threads due to sealer). Try grounding the other terminal on the sender and see if that helps. If not try touching a grounding wire to the body of the sender as a test for no ground through the threads. Mike
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By Ol'ford nut - 14 Years Ago
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Did your old sending unit have two posts? One thing to be carefull of is using teflon tape on the threads. It might keep the sending unit from grounding so use regular pipe sealant.
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By speedpro56 - 14 Years Ago
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56 mercs had a condenser strapped on the sending unit which if not there your unit will not work.
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By speedpro56 - 14 Years Ago
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A ford unit is different from the merc, so make sure it's for a merc.
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By rovison - 14 Years Ago
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The sender I have must be a Ford. It doesn't have a condenser on it. I bought it at Classic Mercury in Ca. and he said it was for a 56 Merc. but I have a 56 Ford and it looks just like it. Its not a grounding problem. Does anybody know where I can get the right sender for my Merc? please help!! thanks, Tom
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By Hoosier Hurricane - 14 Years Ago
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Now I'm confused. The '56 Ford had an idiot light, not a gauge. Does the Merc have a gauge like I think it does? The two types of senders are not interchangeable. I think the condenser Gary referred to was actually a radio noise suppressor. The gauge won't care if it's on there or not.
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By speedpro56 - 14 Years Ago
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John, The 56 mercury had a sending unit very similer to the pickup truck, a fairly good sized unit with a small condenser strapped to it similer to the one used with the gas tank. The 56 mercury unit has two ends coming off it, one for the condenser and one for the ign. wire. The 56 ford is totally different and will not work as it works the idiot light and the mercury works a needle like on a 57 ford.
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By speedpro56 - 14 Years Ago
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I also ment to ad that the mercury does have a gauge.
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By rovison - 14 Years Ago
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Sorry Guys, I didn't know a 56 Ford had a light. The oil pressure sending unit is for a gage. I bought it on line its a Motorcraft part no. B6A-9278-A tested it with con'ty meter worked ok put it in the car and just moved the gage about 1/8". Then I called Classic Mercury they said they have one for a 56 Merc. bought it , tested with con'ty meter, put it in the car and it does the identical thing and it looks the same. I took the wire coming from the gage and grounded to frame and it moved to max. Like I said earlier the engine does have good pressure. Don't know where to go from here! Maybe I still don't have the right sending unit if a Ford is different. Does anybody know where I could find a sending unit that I know is the right one for a 56 Merc. please still need HELP Tom
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By Ted - 14 Years Ago
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Here are a couple of pictures of the ’56 Merc oil sending unit that Gary forwarded to me to post. He mentions again that the oil pressure gauge on the ’56 Merc does not work without the condenser being hooked up to this particular sending unit. 
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By rovison - 14 Years Ago
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Thanks Ted and Gary, Do you guys know where I could find one for my 56 Merc. Do you know the Motorcraft Part. No.? thanks again, Tom
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By marvh - 14 Years Ago
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The B6A-9278-A is the correct part number for a 56 Merc.
If it looks like the picture above it is correct.
The Ford sender units are much smaller and are part number B6A-9278-B.
I think you have a grounding problem with your sender unit. Take a cheater cord with alligator clips on each end or a single booster cable and hook one clip to the base or the rim of your sender unit and hook the other clip to a good ground on the engine block or your negative battery post. Your car should be negative ground. If your oil pressure improves a poor grounding is the problem. Do you have the ground wire hooked from the engine to the firewall?
I prefer not to use Teflon tape on sender units due to the problems like you are having. I use a pipe sealant and only place the sealant above the first two threads.
marv
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By rovison - 14 Years Ago
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Still need HELP!! I tried what Marv. suggested and it didn't change at all. I gounded the sender to the battery neg. I bought a condenser and connected and gounded it with no change!!! I tested wire going into and out of gage and have 12volts at both ends also have 12 volts at connection to sender. The gage does move about 1/8". When I take the wire off and put it to ground the needle goes all the way across some this makes me think the gage is all right. Don't know where to go from hear. thanks, Tom
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By marvh - 14 Years Ago
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Can you look on your sender unit on the hex part above the threads. There should be a number there. That is the pressure trip point of the sender unit. If I remember it should be 7 for 7 psig. .......oops got mixed up with idiot light sender. For a guage sender unit there should also be a number same place if I remember either 50 or 70, that will be 50 psi or 70 psi for full deflection of the guage
Could you post a picture of the sending units you have. It may help us with knowing what you have got.
When you hooked the mechanical guage up did you use the same port on the engine block?
When the key is turned "off" what position does the guage indicate ... full pressure or nil pressure. Turn key on and observe same. Give us a report.
Can you do a continuity test on the sending unit. Test from the terminal to the senders base. It should show an open circuit.
Start the engine and do a resistance test on the sender unit. You will have to pull the sender wire off or you will feed 12V through your meter and might damage it when testing continuity.
Some meters have fuses to protect them, some have reset buttons, others have smoke.
marv
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By shakey pete - 14 Years Ago
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I think that you have the wrong sender you need one that is grd. senstive the higher the oil pressure the more it connects to grd. so the higher the higher the gage will read a condenser on the gage will absorb voltage just like a condenser in a dizzy load it up and give to your friend OOCH ! so find a sender that is grd sensitive weather it,s grd in or grd out just my thought look at uap napa SHAKEY PETE
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By rovison - 14 Years Ago
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  Hi guys, Marv pics of sender. When I hooked up Mechanical gage I DID use the same port. When the key off the gage shows below zero and when I turn the key on it doesn't move until I start the engine and it move about 1/8" up to the zero on the gage. I did do a continuity test on the sender and when I touch the terminal and the base of the sender it doesn't move. I touch the terminal and put a small nail into the base of sender where the oil goes and lightly pushed on the nail with the other continuity wire attached and to show continuity. I haven't done a resistance test yet. I will tomorrow. I'll also take the sender off and see what it says on top can't read it when its on engine. thanks, Tom
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By marvh - 14 Years Ago
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I touch the terminal and put a small nail into the base of sender where the oil goes and lightly pushed on the nail with the other continuity wire attached and to show continuity.(quote)
Be careful pushing a nail into the chamber as you could rupture the diaphragm some are very thin metal others are rubberized.
Do you have another mechanical guage to compare with the one you are using. (I am just trying to eliminate possible areas of errors)
If you get the resistance reading that will give some indications. Set your meter to the lowest range usually 200 ohms for start. Leave the condenser removed when doing the testing.
Did you see the number on the hex I asked about. If you have a sending unit which is rated for 100+ psi or even worse a higher design operating pressure and a guage which is designed for a 50 psi operating pressure the amount of needle deflection will be proportional because guage deflection is dependent upon resistance differential to ground or earth as the Aussies say. A higher pressure designed sending unit will take a higher oil pressure to post a full guage deflection.
marv
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By speedpro56 - 14 Years Ago
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Tom, the number on the condenser which is strapped and grounded to the sending unit is FDC18826-A hope this helps because in the wayyyyyyyyyyyyyyy past when I drove these cars on a regular basis they really wanted this exact type of condenser. If you could just find a good used one it would be worth getting. You would think if all the stars would line up something close would be compatible enough to work ???
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By rovison - 14 Years Ago
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Thanks guys for your help! This is what I found out-- 1) I did a resistance test to the sender and it shows 60 ohms with engine running. Marv. what does this show me? 2) I looked on top of sender, all it says is USA and up with a arrow pointing up and I have it installed that way. (pics attached) 3)I bought the condenser at Advance Auto it is a BWD V10028-------G141Z 4)I ck'd with meter from sender unit post to grd. no reading. 5) I installed another sender no. 75I50 (pic attached) and it shows 80 psi when I start the engine. 6) I ch'd wire from gage again 12 volts. Do you think theirs a resistor in the gage and 12 volts is to much? I have 12v going in & 12 v coming out to sender. thanks Tom   
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By marvh - 14 Years Ago
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rovison (1/21/2011)
Thanks guys for your help! This is what I found out--
1) I did a resistance test to the sender and it shows 60 ohms with engine running. Marv. what does this show me?
2) I looked on top of sender, all it says is USA and up with a arrow pointing up and I have it installed that way. (pics attached)
3)I bought the condenser at Advance Auto it is a BWD V10028-------G141Z
4)I ck'd with meter from sender unit post to grd. no reading.
5) I installed another sender no. 75I50(pic attached) and it shows 80 psi when I start the engine.
Do you think theirs a resistor in the gage and 12 volts is to much? I have 12v going in & 12 v coming out to sender.
thanks Tom
Sender no. 75I50is for an idiot light system. When your engine started your guage went full deflection to 80 psi. Those senders only have off/on trip switch internally.
I did a test setup this AM using a NOS Merc sender and my resistance reading differed substantial from yours, almost 1/2.
For 15 psi I got 30.9 ohms, 25 psi 31 ohms, 35 psi 31.3 ohms, 50 psi 31.4 ohms, 60 psi 31.1, 75 psi 30.7 ohms.
It appears that your sender has too much resistance.
Somebody's going to have to help me on this one if you want to use your own sender as you will have to reduce the ohms.
If I remember some of the things I learned a long time ago is if you add resisters in series you add the sum, if you add resisters parallel it is reduced. I do not know what size of resister you will have to place from the other terminal on your sender and place to ground so it is parallel with the sender unit. If yourresistance is reduced in number your guage will increase in deflection to read a higher number.
The sender I used had the 80 on the square for 80 psi. in an Autolite box part number B6A-9278-A .
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By rovison - 14 Years Ago
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SORRY Marv, My meter wasn't working properly. Got another meter and retested this morning new reading is 25.3 (pic attached). Must be the dash gage coil.??!! What do you think? thanks for all your help, Tom 
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By marvh - 14 Years Ago
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Tom:
Your readings are lower than mine which is the way we want it to go. Do you have another Merc dash or guage that you could use to prove out your car's guage. The cars guage could be the culprit, however it will go 80 psi when using the other sender which should be maximum scale on the guage. Does the guage go below 0 psi as could could be off-scaled and need the needle adjusted to zero.
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By Jeff - 14 Years Ago
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You mentioned that you are seeing 12 volts at the gauge and sender. Since this car is a 12 volt car the voltage you should see at the gauges is 6 volts (if you use a voltmeter you will see that the reading will move up and down, never getting higher than 7 volts). Ford used a voltage reducer on their gauge power feed, when the cars went from 6 to 12 volts, which is a bimetallic set of contacts that opens and closes fast enough to prevent the voltage from getting much past 6 to 7 volts. I would suspect that would cause some inaccuracies in the gauge readings. The reducer is usually mount behind the instrument cluster and serves all the gauges with the exception of the amp gauge.
Why it's not present in the circuit would be anybody's guess.
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By marvh - 14 Years Ago
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1956 was the only year Ford used the full 12 volts on their guages. They did not use a voltage regulator. In 57 they changed to the voltage regulator. That is why the 56 merc and ford temperature senders, oil senders and fuel senders are so unique.
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By rods99 - 13 Years Ago
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does any one know where to nfind the right sender and condenser i have used the same part number and gotten 5 differnt ones please help i have been looking on line and can find nothing any help the only differance is i have a 312 help rod  
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By MontyRay2 - 13 Years Ago
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I have an NOS '56 Mercury oil pressure sending unit. Please e-mail me at glrichards56@gmail.com so I can get your address, etc.
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By jonnireb - 13 Years Ago
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If nothing else works, I believe you could use a '55 guage & sender with the voltage regulator.
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