gas guage problems, help!

[prime mover]

I need some instructions on how to use dual tanks, so far I think the switch controls which tank your reading and the lever controls whick tank your running off of. I filled both tanks up and the "main" only reads 1/2 full and aux reads nothing, I assumed main is the in-cab one so I grounded the wire and the guage went to full. I then switched the sender with the one out of my parts truck and it still reads full. what now?

[bluef250]

Check the electrical switch that controls which tank is registering. Check for continuity through the switch. Only one side of the switch is active - 6 terminals - 2 rows - 3 per side. The center post is the common. The outer posts go to each tank sending unit. See tech article on fuel sending units.

[willowbilly3]

Maybe I missed something but if you filled it up it should read full.

[tubewatts]

yeah that dual tank switch can be troublesome, I often have to jiggle mine to get it to register correctly.....I think it gets alot of dirt in it in that location wafting up from the emergency brake pedal.......

[prime mover]

should I try to bypass it to check for proper operation? are new switches available anywhere?

[prime mover]

yeah when I jiggle it or push in on the toggle the guage changes so I'm on the right track, looking for a new one, anybody have one?

[bluef250]

Did you try fixing yours? See tech article on fuel tanks. I see used switches on eBay occasionally. Have one rebuilt and one used (unrebuilt) if your interested.

[prime mover]

I just cant win, I got a brand new switch in the ford package, installed it and to no avail the guage went up to 3/4 but went back down to 1/2. what now?

[bluef250]

Are the temp and oil pressure gauges working okay? Nothing erratic with them? Does the fuel gauge needle go to full then immediately go to 3/4? Does this condition occur on both tanks? You could bypass switch to confirm that its not the switch. Just remove plug jump from center to either side of the terminals that are lined up. The resistance in the float should be a minimum when the tank is full. If the gauge registers full then goes to 3/4 something seems to be causing additional resistance. That's why the switch gets blamed. As power is supplied something is getting warm or a connection, if not made well, is heating up which increases the resistance. Try the center wire to the gauge and make sure it has good connections both at the gauge and at the constant voltage regulator. Check the wires for bad insulation and internal breaks. By the way, I hate these demon electrical problems. Good luck.

P.S. I talked with a Ford Service Manager yesterday, he suggested that the float may be bad - leaky. I don't know or cannot figure that out as I understand what you described. If the gauge goes to full then to 3/4 full each time you start the vehicle, that does not make sense. If the gauge goes to full, then to 3/4, and stays there then I understand that the float is filling up partially with gas.