Is this truck worth fixing?

My dad has a 1989 ford ranger 4x4 with a 4 cylinder engine… Which they stopped putting in 4 wheel drives. It only has 69000 original miles because it was wrecked and frame was bent. He got the frame straightened and put about 4200 dollars in it to fix it up (back in the mid 90's). He drove it a little while and it started pouring oil down back of engine. He parked it and it has set for over 10 years. I did a little inspecting and discovered it was only the oil pressure sending unit blown apart…(a cheap part). Now the problem. Rats, mice, and squirrels have destroyed the interior and wiring. I mean annahilated it! Is it worth trying to rewire and fix? The engine turns over great and it doesn't start because the fuel pump wires are chewed gone. What's your thoughts on it? Is it worth my time/money to fix and drive it?

Don't try to start it too much, the gasoline in it is probably ether by now. There could also be that in the gas tank. You'll need new tires, maybe had tank or cleaned fuel system, tune up, brakes, coolant flushed and replaced, and it should run fine. I'd fix it up and drive it.

It might be a good hobby car but keep a tab at your expenses. Electrical problems are always not easy to troubleshoot so be patient. If the whole wiring under the dash is gone, it will need a complete rewiring. If you do not have the time, sell it "as is".

I can sympathise with your father after putting a lot of money into it. This was the last straw & the one that broke the camels back. I would be more concerned with the frame than the wire problems. Straightened frames are notorious for bad handling. But I think it has great potential. You should buy new wiring harnesses for it and take your time to get it all right. And fix any other problems it might have. If necessary, for cheapness, you could get used harnesses since these are relatively common vehicles. A camera could help you here. But I would not try to patch the old wiring. It is too unreliable.
But Vincent is right--get it running first. Whether it is worth investing in depends on your other options. You could also possibly get it running and sell it.