need some clarification on electrical testing. continuity to ground?

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.

Mikee gave you some good suggestions except he got the test backwards. When you set the meter to any Ohm (resistance) scale and touch the leads together, it should read zero (no resistance). You use this to check that a particular wire or series of wires and switches are making good connection. Make sure there is no voltage in the wire before you check for continuity. When checking for continuity, you can use any part of the mower frame/engine or the negative terminal of the battery if it is still connected. Once you understand the concept of continuity, you will be using it to test everything from old light bulbs to switches.

You could most certainly use an ohmmeter to test continuity. Set it at the lowest resistance setting, then touch the probes together, (as a pre-test) it should peg out the meter.

To test continuity, touch one probe to the wire you want to test and the other to ground.(Ground can be any part that is directly / indirectly connected to the negative battery terminal, ie: chassis, motor, etc... If you get a high reading, then you have good continuity(little resistance), a low reading will show poor continuity or resistance.

Word of warning though, make sure that when you are testing using an ohmmeter that you are not energizing / completing a live circuit, you'll burn out the meter if current travels through it.

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RE:

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....

Yes they are referring to the grounded terminal of the battery. It is usually the negative but not always. The shielded ground wire is the same potential. Use a car type indicator light not the multimeter. Take one wire to the ungrounded battery terminal to the clip of the test light. When you check for a ground, the light will come on. An experienced electrician might use the meter, but not on the Ohm setting unless the battery is completely disconnected. If an ohm reading is taken to an energized wire, the meter may be destroyed.

Two of the previous answers are good, and the only thing wrong with the first answer is that he said that CONTINUITY is represented by a "high" Ohm reading which is just BACKWARDS.

Ohms represent a unit of RESISTANCE, AND a ZERO Ohms reading would indicate NO resistance AND thus full continuity.

Also, as alluded to in one of the previous answers, high current [Amps] 12 volts will instantly destroy a multimeter. SO... ALWAYS DISCONNECT a battery NEGATIVE [GROUND] cable from the negative battery terminal when trouble shooting with your multimeter, UNLESS you have learned how to use the meter on "HOT" circuits.

When using the multimeter as you describe in your question, DISCONNECT the NEGATIVE [BLACK] BATTERY CABLE from the battery, and attach the black probe meter lead to the disconnected negative cable CLAMP, NOT the negative terminal post on the battery!!!!! I do this using small "test jumper leads" with Alligator clips on each end [available at Radio Shack and most automotive parts stores].

They are two ways to test load to ground. If the battery is properly connected, you can test from load and the ground by using any metal part of the chassis. You can also test the load and using the ground lead of the battery. Good luck...!

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