Could really use some help with finding problem with L3400 Kobota. As a new member

4570Man · Sep 3, 2018

AndyMA said:
Personally using a Multimeter set to DC voltage I would measure from teh actual battery post to a solid frame ground. Should be zero volts. Attempt to start or turn on as heavy load as possible. If it gets much larger than zero you have a high resistance int he ground path from the battery post to frame , Cable and or connections.

Andy
Electrical Engineer

Can you clarify that? I’ve got a truck that doesn’t like to start. I’m pretty sure the frame ground is the problem, but it’s not easy to access.

JWR · Sep 4, 2018

Not to put too many words in Andy's mouth but .. what he was suggesting is to measure the voltage between your battery negative terminal and the frame of the tractor. Of course it better be zero. If you crank your meter up to enough sensitivity you will be able to see the voltage drop across the cables and connections from the terminal on the battery to ground. Ideally that is "zero" (meaning very nearly zero) BUT if you have a lousy connection or a poor quality rusted cable, bum ends on the cable, rusted bolt holding the cable to the frame, etc. you will see the voltage drop being non-zero from the battery ground lug to ground on the tractor (the frame.) You need to find a way to crank the engine WHILE making that voltage measurement so 3 hands are helpful. Cranking the engine WHILE measuring the voltage ensures you have the high starting current running through the ground path at the time of the measurement. That high current will give you the max voltage drop across the ground cable path. If you are an electrical type in the first place, that speaks volumes.

In the case of your truck, this method Andy suggested will certainly prove whether or not you have a good low impedance ground path from your battery negative terminal to the truck ground (or not.)

k0ua · Sep 4, 2018

4570Man said:
Can you clarify that? I’ve got a truck that doesn’t like to start. I’m pretty sure the frame ground is the problem, but it’s not easy to access.

Not only can I confirm and clarify that the measuring of voltage drop across a wire will alert you to high resistance within that wire and/or its connections I will even point you toward a well written article that will explain it even better than I can.

Measuring Voltage Drop - How To Use A Multimeter | Hagerty Articles

buickanddeere · Sep 4, 2018

k0ua said:
Measure voltage on the battery posts directly on top of the posts while assistant attempts to crank the engine. If the voltage drops below 10 volts than the battery itself is likely defective. If the voltage stays near 12 then move out with the voltmeter leads to the starter bolt to see if there is any drop across the positive battery cable. Starter cables can look perfect on the outside and be totally corroded on the inside of the cable under the jacket. So you must determine if it is a battery problem or a cable and its associated connections problem.

Good luck with that advice . I have tried telling people this for years but they just repost with a new list of parts that they have guessed at and replaced .
The general public is about as interested in picking up a multimeter as they are interested in picking up a live rattlesnake .

Xfaxman · Sep 5, 2018

k0ua said:
Yes, and a simple test with a multimeter with an assistant attempting to start the engine would have easily found that problem in seconds. A battery with a high internal resistance will show good voltage without load and will have a severe voltage drop under an attempted load. These types of tests take seconds to perform instead of getting out wrenches and taking batteries in for load testing. You have a perfectly good load tester at hand. It is called a tractor.

It is not enough though to have a multimeter, one must have an understanding of ohm's law and relationship of voltage, current and resistance in DC automotive circuits. I would love to teach the class!.