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

Question
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?

Eric



---------- FOLLOW-UP ----------

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.)

Answer
Onan URL:

http://michaelstractors.com/forum/upload/B112/Onan%20Master%20Service%20Manual.p

The part you need is obsolete.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:

http://www.summitracing.com/parts/rfw-ls11

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.

Eric