Small Engines (Lawn Mowers, etc.): Craftsman 17 HP 42, bench test, coil windings

Question
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Followup To
Question -
Hi,

The lawnmower has the factory safety wiring and has had no alterations; it is five years old now.

My tractor starts but when I engage the mower or release the brake/clutch the engine dies?

I have tried to jumper out the seat and mower and the brake safety switches ( individually ) to isolate the wiring interlocks but to no availe?

The wiring diagram shows dual safety switches but jumpering them will not let the engine start?

I realize this is a safety related system but to replace each component I should be able to isolate which component is not working.

Please reply off line as this is not for the novice to attempt.

Thanks,
Al


Answer -
Trying to jumper the switches rarely works for me...one of those circuits is supposed to be open but the manuals never tell you which one; they rarely show NO (Normally
Open) or NC (normally closed) as regular shcematics.

Do you have an ohm meter?  This works better when you don't know what position the switch is supposed to be in.  You can use to ohm meter to make sure the switches are opening and closing.  When a switch is closed it should read zero ohms.  The switches only have 2 positions, open and closed.

You can also use the meter to check to see if any or which wire is grounded when you engage/release the brake and mower lever.

Let me know if you have a meter.
Eric

Thank you for your reply.

Yes I have a multi-meter and yes I have tested the interlocks.

I found that they are working !?!

But the mower still dies under power; so I started from square one and the coil works intermitentaly and was probably not working under load?

So, I have ordered a new coil and will proceed from there.

Is there a way to bench test a coil?

Thanks,
Al

Answer
Many manuals give some generic resistance tests for testing the primary and secondary coil windings.  The only thing this tests for is open and shorts, not intermitent problems.

We found one intermitent coil this summer.  These problems are the hardest to troubleshoot.  We did the same thing you did...checked all switches and the wiring harness.  We knew the carb, compression and all other components were fine.  Finally ordered a new coil and it fixed the problem.

Let me know what you find.
Eric