Small Engines (Lawn Mowers, etc.)/Onan Engine Part Needed


QUESTION: We have a 1994 Craftsman Garden Tractor with an Onan engine.  It began discharging the battery while running until there was no power.  Sears tried for two years to fix it by replacing part after part (guessing at solution)but could not. We had to buy another tractor instead! A friend is trying now and believes putting in a new 'Low Voltage Sensor' will fix it.  Sears cannot provide the part, Craftsman parts lists indicates 'Not available".  Here are the specs for the tractor:

Craftsman 20 hp Tractor  Model 917.250032
Onan Engine Model 739.11054D   Part Number 127385X on the 'electrical' schematic parts list.
It's a small black box  (4.3 cm X 6 cm)with 3 wires into a "plug" with three flat contact prongs. Printed on it is "???G ELECTRONICS CORP"  Made in USA (that's good!)
You can bring up the engine schematic on the Sears website.

a) Do you believe this is the problem with the discharging?
b) Is there any part to replace this one?
c) Is there a workaround?

ANSWER: The URL is the Onan Master repair manual.  It covers testing regulators.  The manual may not be for your engine but testing the electrical components is very similar on older and newer engines.  If you have a bad electrical part is will usually be open or short and very easy to identify if the part is broke.

I would check voltage drop across the battery cables as well.

Does this make sense?


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QUESTION: First, what URL?  There wasn't one on the answer.  I have looked at the ONAN engine site without luck finding this part to replace.  The man working on it has been fixing mowers for 10+ years so I'm sure he has done the "tracking" of the electrical problem, but I will ask him to be sure.  What can we do to get this part?
We do not live near this individual -- he is 2 1/2 hours away. He mailed us the part he needs. ( He does not have a computer.)

Onan URL:

The part you need is obsolete.  The distributors I checked with do not have the part.

An alternate part that might work is the low voltage sensor from Summit Racing:

Do you know if the technician working on the mower has verified the alternator and rectifier/regulator are properly working?  Do you know if he performed a voltage drop check across the main battery cables?

I have to know the condition of the charging system components and cables to provide better advice.


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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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