Please go at that carefully. There is a lot there which is altered and poorly done, left for the next guy. Check slowly as many of the main power and ground connections as you can. Check for voltages constantly as you check around. Try to remove, cut out, as much of any obvious bad or unneeded wiring as possible. You need to straighten up the wiring, replace the bad connections or connectors.

That battery terminal should be tossed, those are poor and should be temporary only until you can install a much better type. Find those which require a large crimping tool to attach to a good cable. Old cable often have corrosion inside of them. So check for voltage and resistance of all the major wires, such as battery cables. I'd expect to have to replace some of those.

The lights are likely dim due to too much resistance in the main wires and connectors, plus some wires and fusible links. If the fusible links have been cut out, you need to replace them with proper fuses or fusible links. Good luck,

I’m looking for a good detailed wiring diagram so I know where to begin, don’t want to accidentally remove some wiring that I shouldn’t. 

behind the alternator, the metal tab sticking out of the plastic block is supposed to be secured to a stud on the back of the alternator. it might be a necessary ground i forget ATM

the 'temporary repair' battery terminal looks like the best thing you've got going 

red on the ground side can make things confusing

There's enough wrong there in the wiring that you will be at it for a long time. That's why I wrote go slow and carefully. Keep cleaning things and looking it over, slowly you will get an idea of which wires are OEM colors and which are not.

I don't mean to say cut anything not stock, but some things like home wiring don't belong, and the speaker wire seen there could be tossed immediately. You should try to preserve as much of the OEM wiring as possible, that might all be useful later. The aftermarket speaker wire is low cost and you don't know how old or bad anything is.

Fortunately the OEM wiring is not very complicated or difficult to trace etc. You could manage with many different wiring diagrams of similar cars if needed. The basic systems will almost all be very alike between car models. The wiring colors will be the same or very close, which also means you should be able to locate both some old wiring, and some brand new from aftermarket sources. The actual work may require a few tools to make electrical connections etc, so so learn as you go what it's going to take.

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