alternator wiring

[Bill in pa]

On a original M813 alternator, there is a positive, negative and a small wire. what is the small wire for??
I bought a new modern alternator that has 3 terminals.
Positive and the other 2 are I believe field and ignition
I put the red wire to the positive and negative to the case.
I starts, runs and shows 26 volts and dash gauge is in the green
Thanks for any help.

 

[eagle4g63]

The small wire is the "exciter" wire(field wire). It is used to "excite/liven up" the field in the alternator....most new alternators will auto liven up after they get spun to a certain rpm...If you look up a modern alternator wire diagram you will find that the 2 small wire hook ups are as follows: #1: field....same thing as the above exciter wire...hook to a keyed switch or just a toggle. the reason behind hooking this wire up is if for some reason you have luck like me and you don't turn off the field when the truck is not running you will have a small trickle drain on your batteries. The field technically never turns off unless you turn off the power going to it.....#2: is the sensing wire.....now there is a bit of discussion on how to hook this wire up......technically you should run a wire of ample size(depends on the distance...longer needs larger gauge) back to the battery.....it will sense how much load is being put on the battery(by use of lights and accessories) and tell the alternator to put out more or less(amps) if you don't hook this wire up the alternator will just run in max load all the time....not the best thing to do to a battery......as it will over charge them.....Some people just hook this terminal with a small jump wire to the positive stud on the back of the alternator....after all the main wire is running to the batteries.....again not the best because the alternator can't sense what is actually happening back at the battery.

Does all this make sense.....if not let me know and I will try to clear anything up.

 

[Bill in pa]

So all that said,
I need to put the small gauge wire to the field terminal on the alternator. Correct?
Its reading 26.8 when running and 13.8 when running
Its a 8367N alternator.24v 70 amp.

 

[eagle4g63]

Double check the wire with a meter or at least an idiot light....without the truck running make sure there is NO power on the small wire (the one on the truck), with main switch on there should be 24 volts. IF so than yes hook it to the field terminal....then at least jump the other small terminal to the battery so it can regulate how many amps to put out...even though it is rated 70 amp that just means it can put out 70 amp max.....you don't want it to do that all the time.

 

[74M35A2]

Find enclosed a pic of modern HD alternator connectivity. There is no exciter wire anymore, and it seems yours is also working ok without it. The remote sense is typically not required, especially on lightly (electrical) loaded vehicles. The alternator should not go full tilt if the remote sense is left off, as the regulator then simply uses the B+ terminal to set the system voltage. There can be up to a 1V offset by using vs not using the remote sense, if equipped. The sine wave output is tapped into the AC portion of the alternator, and just used to back-date older systems where it was a tachometer or triggered an hour meter to run. These are now "one wire" alternators, needing only to connect the B+ lead. The other connections are purely optional.

Does this look like what you have? The naming is typically same regardless of maker.