First the water pump. There are several types of pumps out there the most common being a ShurFlo. It is impossible to tell you much about how to trouble shoot without knowing just what pump you have. If you cannot read the label a photo will help. Like the others have said make sure your water supply is good, that you have plenty of water to the pump and that there is not a kinked hose on the pickup side. Also check for leaks or open faucets, it may seem obvious but sometimes they are hard to find. Let us know the type of pump and we can help more.
The fuel gauge. you say its not working but how so? Just not showing any level at all? If that is the case find the sender on the top of the tank, with the power on use a jumper to short the wire on the center of the sender to ground. The gauge should read full. if not the problem is in the wiring or gauge. If it does read full and empty when you remove the jumper then it is the sender and you will have to replace that. If it is the gauge you will have to get to the back of the panel. Check that you have power to the gauge. There will be a stud marked + likely with a red wire to it. With a meter or test light check for power. if you have power next find the stud marked S use your jumper to short this to ground. if the meter shows full the problem is with the wire to the sender, if it show empty then the gauge is bad and you will have to replace it.
Good luck let us know what you find
Capt. Wayne Canning, AMS
www.projectboatzen.com