I've got a 1977 toyota pickup that isn't charging. It has a 3 wire alternator - field, exciter, and stator. Probing the connector for the alternator, and with the key turned to 'ON' but the engine not running, I'm getting 12v on the exciter but not on the field. However, the charge light is on.

So at first I thought it was a faulty ignition switch failing to make the correct contact. However, the charge light is powered, so we should still be seeing 12v on the field coil, right? Does that mean its a bad wire? I'm really confused y'all.

What do the line dashes between IG and F mean?

Here's the electrical diagram for this year:

 

I'm not an electrical expert, but only once did I have a charging issue that a new alternator did not fix. The other was because the battery wire on the back broke.

 

The line dashes between IG and F, as well as those between F and E and elsewhere indicate that is a component, in the case of your question, the regulator.

What you are calling the "exciter" is the regulator. Exciters are auxiliary generators (DC) found on large alternators typically found in power plants and locomotives to "excite" or to provide power for the field.

Now if you're getting power to the F terminal of the alternator chances are the alternator is FUBAR, either the brushes (fixable by you) or the field is open. If you do not have power there check the F terminal on the regulator for power . Yes...bad wiring or connectors...No...check for power at the IG terminal of the regulator. If you have power there the regulator is probably FUBAR. (that's my guess) If there is no power on the IG terminal of the regulator check that fuse, the wiring and the connector.

On "Thrill" type regulators the points you see frequently get out of adjustment, burnt or corroded. The coils will get shorted or go open as well.