help need engine wiring for dummies 1966

[blackdawg]

I tried a earlier thread on the general thread site helped a bit but still have too many questions.I have a 1966 chevy stepside.previous po have added after market guages so its a little old and new.then engine is a mid 1980s 350 with hei distributor,th400 transmission.I have added pictures and text.pic 1 five wires from the firewall red,brn,blk,grn,tan pic 2 they run to the horn relay that blue wire is grounded to the air horn.A red wire runs from the relay to the postive battery terminal.negative terminal has a ground wire to the frame and bolted to the engine.there is a splice wires coming mid point from the main harness pic 3.see the thread below it was mixed up off the splice wire plug goes on the top of the alternator.thats the black wire,red wire comes out of the plug i don't know where this goes.off the splice wire there is a heavy blk wire don"t know where this goes.pic 6 &7.postive terminal of the battery goes on the terminal on the starter that i"m sure.pic 4 &5 are of the distributor 3 wires off the plug battery,tach ,does the battery wire go directly to the postive on the relay ? tach goes to the tack,third wird is that a ground ?.pic has two wires what are they for? And the th400 would have a wired speed sensor .any help much appreciated.close to getting the truck started.once the wiring is done clean the tank ,add fuel,oil,transmission fluid

[blackdawg]

from the hei distributor the are 3 wires coming out the plug
one for battery where should i run that one directly,one is for the tach and the third wire is that for a ground? also have two more wire coming from the cap.anybody have any ideas.thanks