I am trying to get the gauge for the rear fuel tank working on a 1970 F 250 Camper Special. The ground at the tank is good, and the wire from the engine compartment to the sending unit is good, but there is no power getting to that wire, from inside the cab. I can see the wire near the fuse panel but not sure how it connects into the power source. The gauge for the tank behind the seat works.

Any advice appreciated....

 

The orange if grounded to the tank or body will move the gauge to show full if it's all working right. So that means the sending unit is not working. The floats do get bad so that maybe it. To test the sending unit when it's out of the tank just put the orange wire back on and have your ign.key on then you ground the unit and move the float arm slow watching the gauge, no movement replace it. I've had to replace two sending units and one float in the passed 30 yr of having my pickup..Hope this helps in some way..
my 2cents..
orich

 

I was first trying to get power to the sending unit before replacing it, in case it might be ok. Need to figure out why the wire for the rear tank is not getting power. Maybe the switch?

 

What about a bad gauge? If the temperature and oil pressure gauges work okay, the CVR is functioning properly. The electrical path is from the CVR through the gas gauge down through the gas tank variable resistor to ground. There will be no power at the float if the gauge is bad.

Ebbtide, check for 6 volts at the high side of the gauge. If you have it, check the low side. Six volts there means a break in the path to the tank; zero volts means a bad fuel gauge.

 

The gauge does work for the tank behind the seat. I was thinking maybe the switch is not sending power to the rear tank. "Communication" between the rear tank and the gauge seems to be non-existant.

 

Take a wire and short over the switch. If you get results you have a bad switch. Find the ground wire, lift and scrub it, and reattach. Grounds have a habit of lifting on the old iron.
We are closing in, Buddy. Report back.

Semper Fi

 

My two cents... Ebbtide, the connection at the sending unit comes after the gauge and is a GROUND side connection. Please stop trying to see power there. We'd all like you to live!

 

Am still here.... There is power at the sending unit for the tank behind the seat, so I figured there should be power at the rear tank sending unit. Not that I felt at ease with a hot wire near a fuel tank.

I undid the electrical tape near the switch, and it looks a bit strange. There are three black wires that are taped together, and a green wire and an orange wire that are connected together. Then there is green wire with a red stripe, - the the ONLY wire that leaves the bundle of tape- and this connects to an orange wire that connects to two other orange wires - one that goes to the tank behind the seat and another that goes into a harness near the fuse panel. (I took a few photos but not sure how to go about posting them here.)

 

You need a good wiring diagram. I'll see if I have one and if I do I'll post it. Might be one elsewhere on this forum.

 

I found this on line.
Doesn't show our camper special's second tank and all the wiring that goes with it but it might help. Wire # 286 Orange. Note the connector next to the Instrument panel is actually flipped so 286 comes in to the connector on the right but it's corresponding pin is across from it on the left on the instrument panel.

I had the same problem you have but since my outside tank had a hole in it, I removed the old corroded connector and bypassed the switch and everything started working (for the front tank)

http://www.fordification.com/tech/wi...-70_master.jpg

 

Here's a 72 camper special. Again it's wire 286 Shows everything! Huge file but worth it!

http://www.fordification.com/tech/wi..._F100-F350.jpg

 

Thanks for the wiring diagram!

Will work on getting things hooked back up and see what happens. The rear tank sending unit has yet to be tested, but there is a chance it could work.

In the wiring diagram I did not see the 3 black wires that come off the switch. Any idea what they might be for?

Thanks again!

 

Hooked up the wires according to the wiring diagram. (There was a hot wire going to the sending unit on the tank behind the seat, and the wire for the rear tank was connected to the wire that was supposed to go to volt reg.) The gauge works for the tank behind the seat, but for the rear tank it stays pegged past full. I have cleaned the ground and the connections already. Does this sound like the sending unit, or wiring?

 

man i cant find a book to help me any weres for this truck of mine its a 1970 ford f100-250 not sure its 4x4 with a 300 straight 6 but i dont know were the orange wire go"s for the fuel gage in my cluster i know its like beating a dead dog but can some plz help me and hell me were this thing go"s my dad told me it go"s up to the cluster that cant be right were in the hell dose the wire go if you now or have a wire digram plz help a bro out lol

 

Power flows from the fuse to the gauge, to the switch, to the tank unit, then to ground.

Checking for power at the tank unit is a perfectly valid troubleshooting technique AS LONG AS THE WIRE IS DISCONNECTED FROM THE TANK UNIT. You didn't say whether you're lifting this wire first, or not. What happens to the gauge when you disconnect the wire at the troublesome tank?

So the gauge has a "power" side and a "ground", or "contro" side. Power comes from the voltage regulator (which isn't really a "regulator" at all; it's a bimetallic switch that opens and closes depending on the current flow through it. The result is that the gauges get either 12V or zero volts, which sorta averages out to about 6 volts). Anyway, no current through the gauge makes the gauge read "E", witnessed by the fact that it goes there with the key off.

So. If no current, or low current through the gauge means it shows "E", then more current through it would make it read higher than "E". The amount of current is controlled by the variable resistance supplied by the tank unit.

If the tank is empty, the float is at the bottom of the tank and the resistance is at its maximum. With a full tank, the float is at the top and resistance is at its minimum. Note that this resistance is in respect to ground.

You said that when you select the suspect tank, the gauge reads "F". That tells me that there is a low resistance to ground on the ground side of the gauge.

I'd look for wires that are shorted to ground, a bad tank unit, or something like that. IOW, if the gauge reads "F" all the time, it's not a problem with the tank ground, it's a problem with a low resistance to the gauge with that tank selected.

Your problem is either at the switch, somewhere between the switch and the tank, or a bad tank unit. Sounds like maybe Gomer might have done some unprofessional modifications at the switch? I don't know.