I want to make sure that I have my alternator wired correctly. I have a 1980 Brat EA71. I was under the impression that one wire goes to the battery from the post on the alternator. then on the plug of the alternator there is a ground, and a momentary hot, to excite the alternator while in start.

 

Well, I'm not getting any juice that way. I found that if I take the wire which I believe to be momentary during start, and move it to hot in run continously, I get 14.5 volts.

 

Is this correct? Is the wire from the plug on the alternator supposed to be hot in the run position, or in the start? I haven't seen an alternator hooked up to have the exciter wire in the run position, but then again, it's a subaru. It seems to be correct, but I don't want to fry anything.

 

Thanks in Advance.

I'm assuming you are trying to install an internally regulated unit? A stock '80 Brat would be externally regulated and I can't remember off the top of my head how those connect through the external regulator....

 

For the later internal regulated alts ('82 and up):

 

Standard GM remote sensing system.

 

Big wire goes to the battery positive.

 

Next smallest wire goes to the main power junction point - this wire senses the voltage at the junction and allows the alt to regulate power at that point to account for any voltage loss between the alt and the junction.

 

Smallest wire is the field excitation/warning lamp wire. It connects to battery positive and has a dash warning lamp and a diode inline with the wire. Anytime the voltage is higher at the battery than it is at the alt the lamp will glow. When the alt is making power this is not the case so the lamp is dark. This wire is also the field excitation wire that gives the windings their initial magnetic field so the alt can begin producing power. This wire isn't totally necessary as the alt will self-excite once it hits about 2500 RPM or so. Bu it's a pain to wrap the engine up to 3500 every time you start it.

 

GD

The exciter or the commonly called L (lamp) wire is always tied to the battery through the charge warning indicator lamp and ignition switch. When the switch is ON, current is applied from the battery to the alternator connection in order to get the excitation process going when you start the car. There still is voltage from the battery present when the alternator is running but the current in the circuit drops down since there is voltage now also present from the working alternator. The color for the exciter wire is usually wht/red.

 

Like GD mentioned, the other small lead ties to the battery also for the regulator circuit. Along with the main output lead, all of these leads are on fused circuits so in case something shorts them out there is protection.