Hi
My 1948 f-1 was converted to 12v by the previous owner along with all the dials.Nevertheless a fuel gauge was never fitted.
Problem is i do not know if the fuel sender is a 6V or new 12V....!!
Is there any way to tell if its 6 or 12 and is there any way to test if its working before i buy a dial.

Thanks
Dusty (uk):-X12

 

[updated:LAST EDITED ON 08-Dec-02 AT 10:47 AM (EST)]An automobile electrical shop (alternators, batteries, speedometers, etc.) should be able to determine 6V or 12V without much difficulty.

Regarding the bed, try logging onto www.lmctruck.com or www.rbsobsolete.com. LMC is the less expensive of the two. I did a Keyword search using "1948 Ford Trucks" and got a few sites...

Daryl

 

I'll take a stab at answering this question but am not sure if this is a correct answer.It is my understanding that a sending unit is nothing more than a variable resistor. If this is the case then I do not think it matters if it is hooked to 12 volts or 6 volts. It should work with either. I am only assuming this and maybe someone who has an electronics background can give you a better answer.

I can however tell you how to check if the unit works. Using an ohm meter Connect one side to the metal bracket of the sender and the other side to the terminal on the unit. When you move the float arm up and then down the resistance should change. If there is no change in ohms then the sender is defective.

This is the best I can do to answer your question but there must be another member out there who can either validate my theory on the 6 to 12 volt part of your question or give you a better answer.

 

hi
Thanks for your input but I have been told by someone else that 12v will damage it if its a 6v unit!!! he may be wrong
I have also noticed that there are 6 & 12 volt senders in some catalogs so I guess there must be some difference..
Anyone else with some ideas..
Thanks again
Dusty

 

I too am dazed and confused on this one. I believe that theoritically it should not make a difference if they are 12v or 6v that they work off of resistance. Yet have seen the 12v and 6v sending units for our trucks. I believe the online store offers one either 6v or 12v.

Would apprecaite any insight by someone much more electrically literate than myself since this is my next purchase.

Tim

 

Regarding voltages and fuel guages, it has more to do with the guage unit itself than the sender. The sender is in fact just a potentiometer and could really care less how many volts you put to it - within reason. 12 volts won't hurt it a bit and neither would 24. The guage head is a different story. If you apply more than the rated voltage, you'll burn the coil up. The reason that the senders are probably marked 6 or 12 volts is due to their resistances. One is calibrated to operate a 6 volt head and the other a 12. The sender and guage head must be matched to maintain the accuracy of the guage. Nearly all the OEM manufacturers sender resistance specs vary quite a bit. If you try to run a Chevy guage with a Ford sender, It would read way off. Ditto for vice versa. The same holds true for 12 to 6 volts.

Batman

 

"Ahhh, if only things were so simple." - D. Franklin

I made the same mistake of assuming the gage and sender were simple resistors. For the 1956 model year, at least, they are not. Both use bi-metallic strips and heating coils (resistors) to send and display the fuel level. The shop manual has a section on testing the gage but is a little skimpy on the sender. It also has a complete circuit diagram. Remember, this is all for 1956 (12 V) although it may apply for a number of years around that year.

To test the gage:

Apply 3 VDC to the gage terminals (make sure the polarity is correct). The gage should read about 1/2 scale. Apply 4.5 VDC to the gage terminals and the gage should read about 3/4 scale. You can use just about any kind of 1.5 V batteries for the voltages and combine them to get either 3 or 4.5 V.

To test the sender:

Check the gage. If the gage is OK then check the wiring from the gage to the sender. If the wiring is OK the sender is bad.

That's a summary of what's in my shop manual. If yours has the same bi-metallic strip-type sender it actually sends pulses of current from the tank to the gage. The gage averages out the current in the pulses.

The best advice I can give you is to go ahead and buy a 12 V gage since your truck has been converted and the other gages are already 12 V. When you get the gage, hook it up and either it will work or not. If not, replace the sender with a 12 V unit. Sorry - can't think of an easy way to test the sender without a working and calibrated gage.

On my truck the original gage and sender have apparently been replaced by some aftermarket stuff. After messing with the replacements they seem to be simple resistors - NOT like the originals.

 

????? Ya don't say! I've not yet run across one of these. Guess ya learn something new every day. Thanks for pickin' up my slack, George.

Batman

 

Yeah Rage, I was very surprised too until Mr. Franklin and Kenny got me straight. Corrected me after I put up a long, detailed post explaining how to test a variable resistor sender/milliamp gage setup. They are both real gentlemen of the first order - could have told me I was full of $h|t but were very nice. Just wish I hadn't been such a bonehead and had looked in my shop manual more carefully before posting. Not that anyone who's posted on this thread so far is a bonehead at all. It's just one of those things that seems so obvious until you see what Henry actually had his engineers do.

 

hi Guys
Thanks for all your help

I will have a go at the weekend.
Thanks again

Dusty:-X12

 

George has it right. My 49-51 shop manual describes the same calibration test for the gage. You put 1.5 volts across the gage to get 1/2 scale. It doesn't say it, but I guess 3V would give you full scale. Disconnect the sender unit during the test.

This type of system has two advantages, it levels out the signal so the gage wouldn't swing when the fuel sloshes around and most importantly, the readings won't change as the voltage changes. In theory, you don't need to do anything when you go to 12V. The current through the gage and the sender are the same. At 12V, things will heat faster and the sender will click on and off faster, but the gage will just follow along. I would measure the resistance of the gage, double this value and put a resistor close to this value in between the sender and the gage. This will keep the current at the original designed range and not risk burning out either unit. (Remember the wattage of the resistor needs to be adequate for having 6V across it. P = V*V/R = 36/R.)

BTW, the oil pressure and engine temperature gages work in the same way. A V8 has two temperature senders. Being insensitive to voltage changes with these old generators was important. Modern cars have a voltage regulater for the gages so they run at a constant 12V while the charging system gets up to 14V.

Johann