Frequently Asked Questions...
need some clarification on electrical testing. continuity to ground?
i've been having some minor issues with my John deere lawn tractor that i posted a question about yesterday or so. i have a repair and service manual and have been studying and learning the electrical aspects of the mower. i've learned a lot about how it's wired, what goes where, etc. i'm gonna have to start testing wires and connections to get down to the bottom of what's going on.
Now what the question is....
a lot of the tests are testing continuity to ground. lets say for instance; check 945 white wire for continuity to ground.
what "exactly" is the ground part of it. are they referring to the negative post of the battery, the shielded ground or what.
This whole ordeal has turned into the more i know, the less i understand. I have a continuity tester.
I also have a multimeter, and if i'm correct can use the ohms setting to test for the resistance, which is also sort of like continuity???? just a little confused
if you can help me at all, it would
Answer:
Hi Michael.
I have been designing the electrical circuits for Briggs and Stratton for 50 years, so I understand your problem.
Ground is either -ve (negative) battery post, or the chassis of the mower to which the -ve battery post is bolted to via a 16mm black cable. Basically, the whole machine is the -ve battery return or ground.
Any cable (or wire) that reefers to ground should be 0-Ohms at either end (short circuit). If not then an open circuit means that the equipment will not function as the circuit is 'open'. This condition is unlikely to occur as most equipment on your mower is grounded to the battery via the mower's body (chassis). The only circuit not grounded directly (it is grounded indirectly via a cable) to the body is the lights; where a cable will feed (12 +ve) the each light (in parallel) and the earth (ground) wire will run back to be bolted to a main earth bolt located somewhere on the chassis. It does not matter where on the chassis this earth bolt is situated. As long as the bolt and nut are clean and the hole around the bolt is bright to the metal giving a good cable (wire) to ground contact, than all is well. A light smear of petroleum jelly is good here, as too, on the battery terminals.
Most problems arise from vibration. An insulated wire will often weaken through flexing and break, making an open circuit and power to that circuit will be lost. Test for continuity (0-Ohms) at either end of any wire and replace or repair as required.
Often the wire feed from the ignition switch to the solenoid will break inside the insulation and cannot be seen with the naked eye.
The starter motor will often run on 9 Volts with a resistor in series (depending on model) so that the voltage drop on the battery will turn the starter. Test with the low Ohms setting 0-200 ohm range.
Open circuit will show up as infinite resistance. A short will show up as 0-Ohms (zero) and the correct resistance (all being well with the internal resistivity) about 10 Ohms).
You starter motor is a different matter, as you will not have the best type of meter to test the circuit.
Either you put 12 Volts directory to the starter germinal and the stater functions correctly or it will not function at all.
Often the ignition switch becomes faulty and in need of replacement; they are cheap enough.
The small black ground wires running closely round the engine might need some inspection for open circuits here, as they can be damaged, so check for continuity on these, too. The ignition switch offers a ground to these to stop the engine. Often as not these wires get their insulation damaged and ground themselves on the engine housing. they should only be grounded when the ignition switch is in the OFF position.
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