Fuel guage quit working and other issues

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I have two different 92 Explorers. The first is pretty easy. The fuel guage stopped working on the previous owner. He said it worked sometimes then just quit altogether. My question, is it the unit in the tank that's faulty or in the cluster? It is a 4.0 auto just for reference.

My other Explorer, which is 4.0 5-speed, had been sitting without being started for about 8 months. The battery was dead so I tried to jump it but it just wouldn't jump with the battery so dead. I tried grounding the jumpers on the alternator and of course threw a little spark since I didn't disconnect it from the other truck. After that is when my issue started to occur though. The issue is, when engaging the key to the start position, nothing happens. There is power throughout the truck and the brake light comes on when you turn the key forward. I replaced the solenoid and that seemed to work but only for a few tries. Then it started doing it again. It will start by jumping the solenoid. Also, after running, the temp and fuel guages pegged out even though I know there isn't that much gas in it and I know the engine is not getting hot. My thoughts are, possible bad clutch safety switch, ignition switch, or some bad wiring. Anybody have any other ideas? It should be noted that it appears some mice decided to inhabit the engine compartment some. All that I've noticed is the heat pad around the HVAC is torn up with some droppings on top of it. I haven't noticed anything inside the truck itself.

 

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Update on second truck:
I went through all wiring behind the dash and in the engine bay. There is no damage to any of the wiring. So something somewhere is not getting a good connection between the solenoid and the switch. The truck has power at all times, battery is charged. When I let go of the key, it makes a click under the hood, don't know what that means.

So, I'm leaning to the clutch safety switch or ignition switch. But, I don't understand why it works sometimes but not always. How can I test these?

 

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Update 2:
Just so it's known, I did finally figure out the culprit. One of the prongs on the clutch switch was bent. It was against another prong and the connector wasn't plugged in all the way. As for the fuel guage, I imagine it's pegged because the float is frozen. The tank has a hole in it towards the bottom so I can't fill it up all the way. Still don't know what's up with the temp guage. I haven't let it run yet today to see if it pegs out again. If I remember correctly, I didn't put a thermostat in it so that wouldn't be the issue. Like I said, it doesn't seem hot at all, the coolant isn't bubbling as though it's hot or blowing over to the overflow. It's 30 degrees outside here too. Any ideas on that and my first truck issue mentioned in the first thread?