Installing a new fuel sending unit

[Randy1944]

On my 1939 Ford Pickup, the fuel sending unit or gauge is not working. I have a new sending unit and started to install it to replace the old unit. The directions say that a ground wire is necessary. The old unit had no ground wire(of course it didn't work either). The directions said to hook ground wire to frame. I just wanted to ask if a ground wire is necessary?
Thanks

[adileo]

Originally Posted by Randy1944

On my 1939 Ford Pickup, the fuel sending unit or gauge is not working. I have a new sending unit and started to install it to replace the old unit. The directions say that a ground wire is necessary. The old unit had no ground wire(of course it didn't work either). The directions said to hook ground wire to frame. I just wanted to ask if a ground wire is necessary?
Thanks

Randy I hate to say this but, I bought a replacement unit from Drake and no matter how I wired it, it didn't work. What I wound up doing is, since my caulk was saturated. I cut it off and then cut the rod that holds the float off of drake unit and had a friend weld it to old sending unit. It now works great.

I have a 39 6 volt coupe

[grovesmr]

You will need a complete circuit. A ground wire may not be needed IF the screws holding the sending unit have a good connection to ground from the unit to the tank and the bolts from the tank have a good connection to the frame. If all these parts have been painted you may not have a good connection.

You can test the sending unit with a voltmeter, you should see resistance change as you move the float arm. With your leads connected to the two contacts on the unit.

If the unit checks out make sure you have continuity to the frame when the unit is installed in the tank from one of the contacts.

If original unit didt have the extra lead that this one does. You can send the ground to anywhere convenient. If original didn't have that extra lead its assuming ground through the unit>tank>frame and replacement may have the unit isolated from the flange which is why it has a separate ground lead

[JSeery]

Some guys seem to get these to work and some can not! The problem is it works entirely differently than the original units. The Ford unit was a pulse type of sender that worked off of a set of points. The replacement units are a resistance type of sender. Either way you need a good ground. If the tank is grounded to the frame and the sender is grounded to the tank it should work. If not it will require a dedicated ground. Should be able to check the grounds with a voltmeter set on ohms.

[grovesmr]

Originally Posted by JSeery

Some guys seem to get these to work and some can not! The problem is it works entirely differently than the original units. The Ford unit was a pulse type of sender that worked off of a set of points. The replacement units are a resistance type of sender. Either way you need a good ground. If the tank is grounded to the frame and the sender is grounded to the tank it should work. If not it will require a dedicated ground. Should be able to check the grounds with a voltmeter set on ohms.

Yep my long winded post basically says it sound like a poor ground connection

[petehoovie]

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I would not replace or discard the original unit until you known for certain that the sending unit is bad. I would do what 'adileo' suggested above. It's what I did to resolve the problem in my '37 and '53....

[flathead 53]

try to keep the old one ,if its just the float its an easy repair ,never the less these old senders can be repaired ,if i spot them at swap meets i buy them they are hard to find .

[grovesmr]

Originally Posted by flathead 53

try to keep the old one ,if its just the float its an easy repair ,never the less these old senders can be repaired ,if i spot them at swap meets i buy them they are hard to find .

definately if its the float just do that, its readily available and the same up until at least the one i replaced on my 1976 f350 last year. its a 10 dollar part. but this sounds like a wiring issue, probably a ground broken between unit and frame

[19Fordy]

Yes, run a ground wire from one of the screws on the sending unit to the frame.

[Randy1944]

Thanks for the info. I think I will clean up the old unit and try to get it to work. Any suggestions as to what to do to the old unit to help it?
Thanks

[petehoovie]

What type of float is on your original unit - is it a cork float?

[rotorwrench]

First you have to test the old unit to see if that is the problem. You will need any King Seeley fuel quantity indicator used by Ford for the 6-volt system, some jumper leads, and a 6-volt power source to connect you sender and test. Many times you can pop the cap off the old sender unit and carefully clean the tiny little point set on the bi-metallic strip then test again.

You will never get full accuracy with the later resistance based units and your OEM indicator. They are designed for resistance based indicators. The King Seeley system is current based. There are many threads on this forum about these systems if you do a search. Probably one every two weeks on the average.

[Randy1944]

The float on my old unit is a brass one and it does float. I tried grounding the old unit and it still does not work. I see no apparent damage with the old unit and I will continue to work with it.