The Witzl's Quick Guide to Wiring an Internally Regulated Alternator

This question pops up frequently, and i've answered it a fair few times, so i might as well post it here.

Internally regulated alternators are found on pretty much any post 1984 Toyota. The easiest way to identify that the alternator is internally or externally regulated is to look in the engine bay for the presence of a voltage regulator, usually bolted to the strut tower and having a standard type 6-pin spade connector.
Here's a pic of an external regulator in an AE71:

If there is no external regulator on the car from which the alternator came, then you should have an internally regulator alternator. To confirm, have a look at the alternator in question, and see if you can find pin identification for the 3-pin plug on the alternator.

It should be labelled something like:
  • S
  • L
  • IG
... and of course will have the large post for power out to the battery, labelled B+ or something similar.

Here is how it is all connected:

  • S = voltage sense
  • L = charge light (on dash)
  • IG = ignition

A few notes.....

# If you do not connect the charge light, the alternator will not charge the battery

# Ensure to use a 60-100A fuse for the battery connection. Fusible links are ghey, dont use them!!!

# If you want to make your life easier when converting a car that had an externally regulated alternator with an engine that has internally regulated alternator (eg. AE71 -> 4A-GE)... then you can use the 6-Pin plug for the external voltage regulator to make wiring easier
-> The 6-pin plug already has the voltage sense, charge light, and ignition wires there.
-> Remove the external voltage reg.
-> Just buy a bare 6 pin plug from Supercheap or similar with the crimp pins included, and use the end that plugs into where the external voltage reg. went before
-> On most old Toyotas, the 3 wires you want are:
-----> White = Voltage Sense
-----> Yellow/White = Charge Light
-----> Yellow/Black = Ignition
.. but check these with a multimeter first! S should have 12V+ from battery, IG should have 12V+ when ignition key turned on... and if you earth L, the charge light should come on.
The following link is the BEST explanation of Toyota Charging Systems freely available on the internet