Any certificated alternator for a light aircraft will have Battery, Field, and 
Ground connections.  That's it as they all use external regulators, whether 
mechanical or electronic.  If you apply 12V to the field, there should be an 
output on the Battery line.  It's that simple.  That's why the regulators are 
usually interchangeable as well.  All the regulator does is sense the battery 
voltage and regulates the voltage going to the alternator field to control the 
alternator output.  So, if you want a wiring diagram, pick out almost any 
aircraft alternator wiring diagram.  They are all very similar as they are all 
using the same fundamentals.  I would suggest using a Plane Power installation 
diagram as their paperwork tends to explain the operation.  The Aux wire on the 
Plane Power alternator that goes to the Aux terminal on the regulator is 
unnecessary and is there to trigger the "Alt Failure" light on the panel or 
electronic display, so your friend's alternator may or may not have an Aux 
If I was going to attempt to diagnose it, first I would check the wiring.  If 
the wiring is correct and has good continuity from termial to terminal, I would 
verify there is voltage present on the Field from the regulator.  If there 
isn't, the problem is in the wiring or the regulator.  If there is voltage 
present on the field line and no output from the alternator, then the problem 
is probably the alternator.
If his alternator is internally regulated, then all bets are off, but they are 
a very simple installation.  With an amatuer built plane, you can't assume 
anything to be correct, so check continuity of everything, right down to the 
crimps on the wire terminators and check that the wiring is actually correct.
-Jeff Scott
Cherokee Village, AR

Sent: Wednesday, March 14, 2018 at 5:27 PM
From: "Flesner via KRnet" <>
Cc: Flesner <>
Subject: KR> alternator wiring?

I'm helping a friend finish a Murphy Rebel with a Lycombing 0-320. We
managed a first engine run but found no alternator output.  He is using
an "Electrosystems ALX8421LS.  Does anyone have a photo or wire diagram
for this alternator so I can check it for correct wiring?  I've checked
all over the net with no luck on a schematic for this unit.  Any help

I managed a 20 minute around the patch flight in the KR today.  Lots of
sun but chilly and very bumpy.  This cool weather keeps the oil temp
from warming above 160 F.   I'd like to see 180 F minimum. Spring

Larry Flesner


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