I bought a 1988 F250 about a week ago. It has dual tanks.
The switch on the inside that is supposed to change from the front to the rear tanks is a little screwed up. I already know that the switch is backwards, so front means rear and rear means front. I know it's not completely broken because when I switch it, the gas gage changes and shows the gas levels in whichever tank it's on.
But... it doesn't actually switch the tanks. It changes the gage, but doesn't make the engine actually use the other tank. It seems to be stuck on the rear tank.

When I bought it, I filled up both tanks. I've been driving it around and have been "switching" the tanks, but the rear tank is empty and the front tank is still completely full. So clearly, the switch is broken and is not engaging the front tank.

What do you recommend I do first? I have no idea how to deal with this.... And if I take it to a mechanic, will something like this be a huge fix that is going to cost me an arm and a leg?

 

Do you have a test light?
Do you here the fuel pump in the front tank run when you select it and turn on the key?
It should run for one second.

 

how long do you leave the switch on the front? mine takes about 10-30 seconds to actually start taking fuel from the tank i switch to. mine may not be normal though.

 

I had the same prob on my 87 Ranger. Dropped the tank the other day and found it to be a bad connection at the plug on top of the tank. Gage worked but the in tank pump did not. So that or the pump in tank is bad.

 

I'm having the same issue on my 89. The gauge reads empty on the rear tank even though it's full, but it continues to pump out of the front tank the entire time. I would think that if the rear tank were disconnected then the front pump would just stop when I switched to rear and the truck would stall after not too long. I jumped the test terminals and thought I heard the pumps switching but I'm going to double check that. I made sure both tanks were full and drove around for a week on the rear, but when I switched the front the tank was empty...and when I went to fill up the rear tank was still full while the front was almost empty.

Since I can drive just on the front I haven't dug into the problem very deeply yet (more pressing things to fix first), but I definitely want to see what the thoughts are on this issue.

 

No this is not true.
If the selector valve is locked in the front position (from the front tank pump running) and you switch to the rear tank and the the rear tank pump does not run then you will still pull fuel from the front tank and the rear tank will remain full even with the front tanks pump not running at all.

The in tank pumps are only used to switch the selector valve and prime the system if you run out of fuel or go up a steep hill.
This statement is from the 1989 Ford shop manual.

 

Thanks for the info subford...once again saving me from my own assumptions

So I will go listen to my pumps once again, and if they are switching then it would point to a stuck selector valve.

 

When I turn the switch I don't hear anything. The only change it makes is the gage.
I filled up both tanks and would turn the switch every day so that one day it was on the front and the next day it was on the rear. But the rear tank is now empty and the front is still full.