make yourself a tester with a 12v interior light and 2 long bits of wire attached to ot with small crocodile clips on ends and a douple of stiff pins you can put in if necessary.
then find you ignition lives and mark them... same with permanent.
crocodile clip the earth to earth on chassis or battery... live, you just touch wires with until it lights bulb... do that on anything your unsure about. switch things on and see if it has a live.. permanent or not. if it doesn't find the wire that does and give it one. If its a case of.. is this wire earth... put a crocodile clip to a live you know is live, because you already tested and marked, or the battery.. and your other wire to what you think is earth. if your light comes on... it is.
keep doing that until you have your wiring marked and all your instruments working.
worst that will happen is you blow a fuse or bulb... have a spare.
did all of mine with this and mine was a right bloody mess. just about sorted now.
if you have none standard accessories take them off.. get all standard stuff working as it should first. then if necessary run a new live and earth for accessories or utilize the now marked wires, that are not in use, to run these things but make sure there all fused.
use masking tape and marker pen to mark as you go.. do the job once, not a dozen times.