Your questions are not dumb. With respect to your truck Sir: I'm sure that there are many hanging wires and miss-wires and ground issues with this kind of Zombie Swap. My advice above, and I think others have said is: Start over. Remove all the previous owners wiring. We all have purchased trucks with PO wiring from hell and we rip it out. You can save the wire if its good stuff and use it to redo if you want to save some money. I have outlined the basic rewire. But you must study up on wiring diagrams and general automotive wiring before jumping in. This is a great group of guys and gals here and maybe someone will go thru every wire with you. But you owe it to yourself to study up, read the advice. You can solve the sender/gauge compatibility with mechanical oil pressure and water temp kits. Amp/Volt gauge should be no problem. Gas gauge could be solved as Cletis said.
I did asked you what exact motor you had. Jeep or ?
You have four good knowledgeable guys helping you and I'm trying to help as well. You will get it done, you are at the right place.
Wire up the ignition to start it up and get it running good, then lights, brake lights and turn signals. Make sure there is oil and water flowing. If you really want to, you can plumb in generic mechanical oil pressure and temp gauges. NO wiring for either. Place them temporarily inside cab or on engine. Be sure there is water in the radiator and the belt is turning the water pump. I'm assuming you are not going to drive it far until it's all done, anyway.
I know several guys here that would like to see how the jeep drivetrain/chassis was installed. (Carl and I) Do the axles/tires stick out past body?
BTW: the fuel sender does not get voltage applied to it, if that's what you said. The gauge does. Be careful how you wire them up on bench. Sender wire to sender post on gauge. 12V pos to pos post on gauge. 12V Neg to gauge case and sender flange. USUALLY!!! Don't know Jeep to Apache.
