The cap opposite the gas tank with the gauge has a wire that is exposed from twisting the cap

SEL is probably on because you don't have gas cap on correctly, or gasket on cap is torn. Gauge not working is separate issue I expect. Could be fuse, bad gauge, bad sending unit inside tank, or broken wire.

mabey its somthing as simple as your gas cap being bad or a cloged fuel filter

Of course, if this came with a manual.....it should clearly indicate the fill orifice. If it is like the one pictured, The end opposite the handle, where the metal end of the pump is exposed on top of the tank, has a filler hole with a filler cap pushed or threaded into it. Twist this off and add the oil until you see it rise to the half-way point on the sight glass. On brand new units, the filler cap will be taped with a small caution tag, warning you not to start the unit without first adding oil. Most units use a high performance, non-foaming, full synthetic 20-50w oil. If there is no sight glass, the filler cap will have a fill level indicator. Do not overfill!

The right side cap comes off so you can add fuel. The crossover hose at the front of the tank lets fuel flow to both sides. The left cap holds the fuel gauge and fits into a hollow hole. The fuel gauge wiring comes out at the bottom of the tank, thru this hole. Don't try to twist the left cap off or you could damage the wiring for the gauge!

What You'll Need:

• flat head screwdriver
• Phillips head screwdriver
• hammer
• open end wrenches
• replacement fuel tank sending unit
  Before you begin, disconnect the negative battery cable to be sure no electrical sparks are possible. You're dealing with gas which is highly flammable!Your fuel tank sending unit is located in the top of the fuel tank, but is accessible under your back seat (or under the carpet in your trunk) on some models. The sending unit will be protected by an access cover, usually held on with a couple of screws. Lift your back seat or trunk carpet and locate the access cover for your fuel tank sending unit. Remove the screws holding the cover in place and remove the access cover to reveal the fuel tank sending unit.
  Safety Note: Gasoline is highly flammable. By removing the fuel tank sending unit, you are opening the gas tank. Be sure there are no sources of spark or flame nearby.
  With the access cover removed, you'll see the fuel tank sending unit right there on top. It will have a wiring harness plugged into the top (this tells your gas gauge how much fuel is in the tank). Unplug the wiring harness and move it safely to the side. If your fuel tank sending unit is screwed or bolted in place, remove the screws or bolts. Some sending units are a "twist-lock" type. They work like the old twist-lock gas caps. You'll see a few notches along the outer ring of the sending unit. Place the tip of a sturdy flat head screwdriver in the notch and gently tap it counter-clockwise. The sending unit will rotate until it's loose. (the picture above shows the fuel tank out of the car to illustrate the fuel tank sending unit's location). Now you can remove the fuel tank sending unit in one piece. Attached to it is a long rod with a float at the end, so you might have to try a couple of different angles to get it out. As usual, installation is the reverse of removal. Don't forget to plug the new sender in or it won't send you anything!
  
  

The gas guage is likely a bad ground to the gas tank. Check the wiring harness where it comes from the body and goes into the gas tank. Likely there is broken wire there. The harness usually has 2 or 3 wires one may be neutral for both the pump and the fuel gauge. or 2 wires each. An Ohm (resistance) tester will show a particular amount of resistance on 2 wires indicating that the fuel guage is working properly as the resistance will be different depending on how much gas is in the tank. You should be able to buy a cheap digital tester for $10.00
It is likely that these wires are damaged close to the tank or in that harness area that is exposed to the elements, perhaps even at the spot where it goes back into the body or where the harness joins to the tank harness connector. Look for broken or corroded wires here. Try running a piece of wire from the body to the gas tank and see if it makes the fuel guage work indicating a bad ground to the tank.

this cap should press in straight down, if it isn't staying the "hooks" may not be properly set-up
NEVER twist it as this will cause damage to the wiring to your gas gauge

Your going to have to drop the fuel tank by running the Van as low on gas as you can get it to make it easier and lighter. Disconnect the filler neck by taking out the four bolts around the gas cap. Underneath you will have to disconnect the fuel lines and the take the two bands off the tank. You will need help to lower the tank if it is still has gas in it. Once you have the tank dropped and out from under the Van you can remove the sending unit. Installation is the opposite.

It sounds like the float on the sending unit is sinking. Don't know what the float is made of, but over time, it will soak up gas and start to get heavy. This would cause your problem. I don't think it's the gauge, but if you want to test it, disconnect the wires at the tank. The gauge will either go to full or empty. If you ground the sending wire, the gauge should respond the opposite way it was. good luck

Well that tells me that someone installed the wrong fuel level sensor. Your going to have to drop the tank and pull the pump and float assymbly out. Then go to a parts store and get a sending unit that has the opposite resistance of that sending unit. Just wait until the tank is empty so its a lot lighter. You can call the parts store or go down and see if there is multiple sending units. The sending units work by resistance, when the tank is full the float moves up and turns a wheel in the sending unit, which either removes or increases the resistance causing the gauge to lower. The sending units either give full resistance at full or no resistance at full and then changes as the level goes down until it does the opposite at empty.