Sick and tired of this being asked so I found my wiring guide I wrote a couple of years ago on the old forum. This is mainly applicable to ADM AE86 and AE71.
KE70 are a little different, noting that:
-alternator wiring setup on a KE70 is different, but colours you need to connect to are the same.
-black/orange ignition wire for coil (may not be black/orange) is on oposite side of engine bay so you need to extend this to the passenger side.
My Wiring Guide for bigports:
Alternator wiring info found here:
(not my work but use as a reference)
ADM AE86/AE71 Passenger side strut tower houses the external regulator for the 4ac alternator. 2 wires from the body side plug required are:
Yellow: Lamp (L)
Black Yellow: Ignition (IG)
Connect the appropriate wires using the diagrams from the link above (wire colours on new alternator plug may be the same as the ones on the car - usually the case if you use a fwd loom). The sense wire (S) is a white wire connected to battery, but I usually tap it into the bolt on strap (main battery feed - usually two thick white wires) as it goes to the battery terminal. Note that I recommend upgrading the bolt on strap wire currently used on your 4ac as the 4age alternator produces a higher output.
*Assuming bigport* When using my info, Refer to Club4AG AE86 ECU pinout/wiring diagram
Other then that:
-give ignition power to positive terminal on coil (usually a black/orange wire which connects to the ballast resistor on the old coil which you can use [I did], but you can make your own relay to power coil using the black/orange wire as an ignition trigger)
-On 14 pin plug, Pin 7 (+B1) and Pin 14 (+B ) can be connected together, and go to ignition (or can come off a relay you used for coil power)
-On 14 pin plug, Pin 6 (Batt) goes to constant battery 12V source (ie wire straight from positive terminal on your battery if you want, fused - 7.5amp should be the max you need). There is a battery power wire found in the passenger side kick panel wiring junction box (big thick white wire). Tap into this instead of running an ugly wire through your engine bay.
For fail safe starting, you may also need to give power to injectors (Yellow wire found on 10Pin plug, Pin 10 (BF)) by joining a wire into the yellow wire and giving it 12V on iginition (again, use the same relay that you may have used for coil, but might be drawing too much current).
There ARE other ways to do it, and probably make it neater and more factory like but that works.
Fuel pump relay setup (if you dont have a factory COR relay).
Smallport:
Most of the above is the same and applicable (obviously look at smallport wiring diagram/ecu pin outs!) except that injector wiring is a little different. They are powered by a black/red (or black/orange - seperate to the black orange on the igniter/coil) ignition wire, you may have to locate it on your loom and give it 12v on ignition. Basically in short, you want to make sure black/orange wire on the loom has 12v on iginition and black/red has 12v on iginition. That way your coil/igniter has power and your injectors have power.
Smallport looms are also very short, will need extending about 60-80cm to make them work properly. It also needs manipulation to make the wires run the correct direction. You can be lazy and go through the a/c port, but this only sort of just works. You can drill another hole in firewall near your heater box, which will then give you enough length to put your ecu just behind your a/c duct/bridge pipe.
This thread should be stickied.