Starting a new thread for less confusion. I still would like to learn how I go about testing all of this as indicated on this thread https://www.ford-trucks.com/forums/1...long-post.html

I know I am going to have to know these things to test my gauges, I googled ..............what are the resistance values for an 1986 F-150 fuel sending unit..............and found this..................The factory 80-86 sending unit is approx 90-10 ohms answered by Franklin 2 on this forum and this thread can be found here https://www.ford-trucks.com/forums/1...nit-wires.html

I found this chart also within this second thread....
which states MOST pre 1987 Fords 16-158 Ohms, not sure if that is such a big difference or should I be concerned with the discrepancies?

I then googled what are the resistance values for a 1952 Ford truck fuel sending unit, read a post here where a fellow (BobJ49F2) has a 48 and I believe he is indicating that his sending unit reads 74 ohms at full and 10 ohms. Thread can be found here https://www.ford-trucks.com/forums/7...ding-unit.html

Can anyone clarify, help me to better understand all of this. It sounds to me as if I need to do nothing with the either the fuel sending unit I have ( which is the original 6 volt ) and the newer 1986 F-150 12 volt gauge ( my truck has been converted to 12 volt ) I plan to use, is this possible?

 

Our fuel gauge in Albatross reads "DNC" on empty with 140 Ohms and right at full with 20 Ohms. I run the gauges at six Volts. The old gauges work on heat and are not polarity sensitive.

The old ones can be checked by applying a voltage. They should read full scale with 3 Volts applied. They should read half scale with 1.5 Volts applied. You can do that with a couple of D cell batteries.

I don't know about '86 Ford gauges.

Did you measure the resistance of your '86 sending unit?

The old sending units worked off of heat also and the measured resistance will not mean much.

 

The stock sending unit uses the The King-Seeley (Ford Stock) principle. These sending units supply a full 6V through the heater wire in the gauge in the form of a square wave with the duration of the "on" being the variable determining the gauge reading. The longer the duration, the more fuel in the tank. It is this full 6v of current which heats the bi-metallic strip in the stock gauge that causes the gauge to read via a small gear train (that may adjustable?). Most after market sending units are simply a variable resistor which sends a constant voltage to the gauge, lessening that voltage as the fuel level goes down. Therefore, the sending units signal doesn't heat the bimetallic strip in the gauge as much. Unfortunately, the calibration of the after-market sending units and the stock gauges don't match up very well due to the differences in the principle of the signal.

 

Thanks for the replies, trying to figure how to measure these things, starting with the basics, cant find anything specific in the way of measuring what I am trying to measure. Still working on it though.

 

The Ford specified testing method is to take the questionable item (sender or gauge) and pair it with a known good mate. For instance, if you question your sending unit, take a known good gauge and pair it with your sending unit. If you question your gauge, pair it with a known good sending unit. Your multi meter is practically useless for testing King-Seeley items.

 

Now I dont feel so bad, Ive been screwing with this thing on and off and I cant get it to do what I think it should be doing.

I dont have a known good unit at this point.

 

Ok I have read enough to see that the King Sealy sending unit just isnt worth messing with so I am off that.

Franklin mentioned in this post ......https://www.ford-trucks.com/forums/1.............that The factory 80-86 sending unit is approx 90-10 ohms. They make aftermarket sending units which are 78-10 ohms which is close enough.

When Franklin mentions aftermarket does he refer to Napa sending units, I am guessing that is the case since I picked one up this A.M and it reads 74.5 down to 10 Ohms.

I am assuming he is saying this will work with my factory 1986 Gauge and read properly. Am I reading this correctly ?

 

I just called the local Ford dealer and sure enough the gauges carry the same part # from 1980 -1986 on all lines of trucks from F-150 - the 350 series, if that is the case than I guess it would be safe to assume that since the gauge and the sending unit has to be paired that no matter the drivetrain wether it be 6 cyl or 8 the gauges and sending units would all carry the same values. What do you think ?

Clearly the sending units are not identical, I have pulled enough of them now to see there appearances vary but that would be on account of fuel tank changes such as size, pick-up location whatever.

Anyone care to add too or dispute this info?

 

Fuel Tank Sending Unit Tech - FORDification.com

 

That is correct, all the sending units for the 80-86 are the same for all the trucks, because they all used the same gauge in the cluster. The differences you are seeing are;

1. The plain jane style for the small holed gas tanks for all the regular carbed engines like the 300, 302, and 351w, 351m, and 400.

2. You have a different style for most of the 460 carbed trucks, which had electric fuel pumps in the tanks. These will have a return line also made into the sending unit, and provisions for the electric pump to mount.

3. You have the diesel units. These look much like the 460 units with the return and supply lines, but they do not have electric fuel pumps hanging on them.

4. Then you have all the units starting around 85. They went to the large hole tanks, and this is when they introduced the fuel injection on the 302, so that was another added unit, with a in tank pump to supply another pump for the fuel injection. I believe someone mentioned that even though not all trucks required the larger hole for the fuel pump to enter the tank, they enlarged the hole on all the tanks, so that required a across the board change to all the sending units.

When I mentioned "aftermarket sending units" in a previous post, I was talking about the stewart/warner type guage, and most other aftermarket gauges seem to use the Ford style ohm readings.

As far as your original six volt sending unit, I believe you have abandoned that idea, but I am not sure if it was made clear how they worked. Using a simplfied explanation, the sending unit on the old trucks worked like a turnsignal flasher. As soon as power was applied to it, it had a bi-metal set of contacts that heated, and open, cooled and closed, and cycled just like a turnsignal flasher. The float arm of the sending unit put physical pressure on this "flasher unit", and that changed the rate at which it flashed on and off. As someone mentioned in a previous post, this changed the "average" voltage that the gas gauge would see, and make the needle move to the appropriate place. I found this out the hard way myself, I had a old 53 f100, and I ended up getting a aftermarket gauge and sending unit from JCWhitney, and making a adapter to fit it to the original tank.

 

Thanks Dave, let me run this scenario by you, it is where I am at right now and am thinking I am on the right track.

I am using the 80-86 gauges, I am using the original 52 F-7 fuel tank, I need to find a sending unit for that upright tank, as I am sure you can understand that 80-86 sending units just are not going to work because of their configuration.

Ford used its last behind the seat up-right tank in 77 so I am thinking that I need to try and get one of these units. I am not sure what the original capacity was for the F-7 fuel tank, I looked in the shop manual and they are using alphanumeric codes to describe the models but I think it may be 20 gallons

Looking at this chart it would seem that the Ohms reading would be the same for these sending units and should match the gauges that I plan to use in my truck.

I believe that in 77 they had a 19 gallon tank behind the drivers seat available but still need to confirm this.

That may be as close as I could wish for, worse case it sounds to me would be that it will read empty when I still have about a gallon of fuel in the bottom of the tank.

I understand that there will have to be some modifications to the top of the sending unit to have it bolt to the top of my tank but I dont think that will be anything too extreme.

 

1977 cabs were wider than the '48-52 cabs. That may mean the tanks were wider too. (I'd have to go measure mine) that would make that thought kinda moot.

IMO, I'd go with the original tank, original gauges, and original sending unit. And go with a Volt-A-Drop or something to step down the voltage from 12 volts at the battery to 6 volts at the dash.

 

Let me add to my previous statement: Except for '55 and '56, Ford used 6v gauges up through 1979 (maybe longer), and used an inline voltage regulator between the battery and dash. Ford sending units were typically 10 ohms full, and 73 ohms empty, and measuring this with a multimeter should clarify what you have. That said, I see no advantage to using any tank other than a stock original, if it's going to stay in the cab. Keeping the stock gauges simplifies the mounting of gauges in the dash. That leaves one last thing: an inline voltage regulator. Wire it in, get a good ground to it, and you're done. Simply buy one for a Mustang II, install it, and then move on to the other issues running 12volts will create.

EDIT: MII's are bi-metal, not solid state, so going from POS ground to NEG ground won't matter.

EDIT #2: I don't understand why you would want to use '80-86 gauges?

 

I dont have any of the original gauges and you might understand better what I am up against if you could find the time to read some of my previous posts. No problem though and thanks for taking the time to post anyway

 

True, I've been awfully busy lately.

It's just that I think it would be easier in the end to buy an original gauge cluster, since they're the same throughout all models F1-F8 for '51 and '52, and should be plentiful. But I'd be the first person to say, "it's your truck and you can do what you want with it, and who am I to say different, but to offer words of encouragement."