Fuel Gauge Ground?
Thread Starter
|
Posting Guru
Joined: Aug 2003
Posts: 1,243
Likes: 0
From: Michigan
Fuel Gauge Ground?
I have a 56 F100 with a No Limit 17 aluminum tank and a set of AutoMeter Gauges with a older Ron Francis wiring system.
Everthing except the fuel gauge works. All the gauge lights work so I'm led to believe the gauge ground is fine. The terminal that has the fuel gauge wire from the tank to gauge seems to have no power. If I run a wire from ground (it was a test light) to this terminal the gauge goes to full. WHY!!! I would think it should blow a fuse if I run a ground to what is suppost to be a live terminal.
Is the fuel tank ground bad ? I really don't understand how it could be but you never know. If it is bad I will have to take half of the bed apart but thats life with these old trucks.
Thanks, Chuck
Everthing except the fuel gauge works. All the gauge lights work so I'm led to believe the gauge ground is fine. The terminal that has the fuel gauge wire from the tank to gauge seems to have no power. If I run a wire from ground (it was a test light) to this terminal the gauge goes to full. WHY!!! I would think it should blow a fuse if I run a ground to what is suppost to be a live terminal.
Is the fuel tank ground bad ? I really don't understand how it could be but you never know. If it is bad I will have to take half of the bed apart but thats life with these old trucks.
Thanks, Chuck
Postmaster
Joined: Jun 2004
Posts: 4,190
Likes: 2
From: Riverside, So Cal
My 56 still has the stock in-cab tank, but I use an Autometer gage. I have had to debug a number of issues with that setup, including a calibration of the sender.
I think your initial diagnosis is correct. You have a bad ground wire to the sender. Power runs TO the sender from the gage. The fuel sender is just a variable resistor (rheostat). Grounding the power lead to the sender SHOULD give you a full tank reading. The sender ground wire could have a break in it or a bad connection.
Happy hunting!
I think your initial diagnosis is correct. You have a bad ground wire to the sender. Power runs TO the sender from the gage. The fuel sender is just a variable resistor (rheostat). Grounding the power lead to the sender SHOULD give you a full tank reading. The sender ground wire could have a break in it or a bad connection.
Happy hunting!
Posting Guru
Joined: Apr 2004
Posts: 1,908
Likes: 2
From: Seattle WA.
Sounds like the sender is bad, the reostat inside is shot the sender gives off a different level of resistance to ground as the arm moves. When you grounded the unit you supplied the same resistence the sender would if the tank were full. The only other thing that I know could cause that problem is if the tank, or sender housing to tank doesn't have a good ground.
The sending unit does not have any 12V positive power going to it, the positive is supplied to one side of the gauge. The wire going to the sender is a grounding wire and the sender varies the amount grounding resistance to cause the fuel gauge to move. If 12V positive power were supplied to the sender you would have a potiental hazard due to a spark especially if the tool carrier above the tank touched it.
Hope this helps
Rod 51F1
The sending unit does not have any 12V positive power going to it, the positive is supplied to one side of the gauge. The wire going to the sender is a grounding wire and the sender varies the amount grounding resistance to cause the fuel gauge to move. If 12V positive power were supplied to the sender you would have a potiental hazard due to a spark especially if the tool carrier above the tank touched it.
Hope this helps
Rod 51F1
Last edited by 51ford fan; Mar 11, 2006 at 01:38 AM.
Thread Starter
|
Posting Guru
Joined: Aug 2003
Posts: 1,243
Likes: 0
From: Michigan
Fixed it. 
Cleaned up ground still didn't work so I removed the sender it seemed to be stuck. So I cleaned it up and reshimed the mounting and also screwed around with the float arm length and now it seems to read what i'm guessing is close to correct.
I had this sending unit in my stock tank before I installed the rear mount tank so I guess it must have had a small amount of old semi dry gas around the pivot.
Lesson learned: If installing a rear mounted tank make sure the gauge works before installing bed floor even if it is a sheet of plywood cut into three sections it's still a pain.
Chuck
Cleaned up ground still didn't work so I removed the sender it seemed to be stuck. So I cleaned it up and reshimed the mounting and also screwed around with the float arm length and now it seems to read what i'm guessing is close to correct.I had this sending unit in my stock tank before I installed the rear mount tank so I guess it must have had a small amount of old semi dry gas around the pivot.
Lesson learned: If installing a rear mounted tank make sure the gauge works before installing bed floor even if it is a sheet of plywood cut into three sections it's still a pain.
Chuck
