I have a 86 Silverado with duel tanks. Both tanks have been replaced with new floats but the gauge in the dash will not work. I can ground the wire going to the gauge will move to the full mark. But when I plug it back in it only shows a 1/2 tank sometimes. I think it's a ground problem but I don't know where to look. Both tanks work and they do the same thing, The switching valve seems to be ok. Just about ready to give up. Any help please. Thank You

 

Something is cross-threaded somewhere. When you ground the gauge feed wire, the dash unit should show empty; on the other hand, full with an open circuit.

Allan

 

Thanks . I was backwards