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I am changing the alternator on an old tractor. The old alternator has one D+ terminal that receives power only when the key is on. The new alternator I am retrofitting has an S (sensor) and L (lamp?) terminal.

From what I can understand, the wiring for the new alternator is as such;
S terminal to B+ (battery positive post)
L terminal to wire that fed D+ on old alternator (for the purpose of dash lamp)

If hooked up this way will the sensor wire drain the battery over time when the tractor is not running?
Will the dash lamp go out as it should when alternator is making sufficient power?

Any help would be much appreciated,
Thanks guys!
 
Is the tractor positive or negative earth?
Sensor shouldn’t do anything until the key is turned.
Negative earth, from what I understand the 'L' terminal receives power from the ignition switch - through the dash lamp - to excite the alternator and then becomes powered and current stops flowing and the dash lamp goes out. Is this correct?
 
Was it definitely an alternator before and not a dynamo?
 
The 'L' terminal receives power from the ignition switch - through the dash lamp - to excite the alternator and then becomes powered and current stops flowing and the dash lamp goes out. Is this correct?

Yes this is correct on systems where there is no direct connection from switched positive to the alternator, a.k.a. 'machine excited' alternators. The name comes from the fact that there are separate diodes to power the excitation directly from the stator once the machine is running, rather than drawing power from a switched positive input. Not all alternators work this way though.

will the sensor wire drain the battery over time when the tractor is not running

A well designed battery-sensed regulator takes minimal current through the sense lead and will not cause the battery to discharge appreciably faster than it would self-discharge anyway.
 
Yes this is correct on systems where there is no direct connection from switched positive to the alternator, a.k.a. 'machine excited' alternators. The name comes from the fact that there are separate diodes to power the excitation directly from the stator once the machine is running, rather than drawing power from a switched positive input. Not all alternators work this way though.



A well designed battery-sensed regulator takes minimal current through the sense lead and will not cause the battery to discharge appreciably faster than it would self-discharge anyway.
That's great news, thanks for your help Lucien Nunes.
 

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