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Tractor Talk Discussion Forum

Electrical Troubleshooting

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08-13-2012 22:53:22

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Troubleshooting anything on a machine can be a PITA, but electrical problems have to be the worst....especially when no diagram is readily available, and the customer needs the machine running ASAP.

Looked at a machine today for a customer that was having electrical issues that wouldn't allow the parking brake to release. They had taken it off the trailer at the job site and parked it and when they went back to move it a little later it wasn't right.

Based on what I could see and test I didn't have voltage at the parking brake switch, and that traced back to no voltage at the fuse block. Checked the posts on back of the ignition switch and had voltage there....but still none at the fuse block. No schematics to be found, but I was finally able to talk to another mechanic, at a rental yard, that had worked on more of these machines than I had. He told me a few other things to check that were on some machines and not on others. In other words, I was still 'on my own' in that he had never seen a diagram before either, and, like me, was just making a semi educated guess also. Anyway he said the fuse block is USUALLY fed directly off the switches ON post, but sometimes through a relay on the other end of the machine. So, I got back to the machine, check that there were no relays, etc, I missed previously, and then traced the wire as much as possible, again. Again I found no burned places, or anything else that would indicate why it wasn't carrying voltage from the switch post, where I had 12V, to the fuse block, where I didn't.

Finally decided to just pull the ignition switch out of the dash and 'bench check' it, even though it appeared good in the machine. When I went to disconnect the wires off the back the one feeding the fuse block didn't come off right. Instead of the whole spade terminal coming off, the wire and the crimped part of the terminal pulled out of the factory heat shrink insulating it, while the spade part of the terminal stayed on the switch.

Seems the terminal end was broken and the switch, which wasn't good and tight in the dash, had moved just enough when turned off to tighten up the wires and pull the two broken ends of the terminal apart. Being in heat shrink they probably would have never moved back together...and thankfully didn't or an intermittent problem would have been an even bigger PITA to find.

Things like this will drive you nuts. Voltage everywhere it's supposed to be, up until the problem point, and nothing apparent wrong until there. Had I not gotten to my wits end about 5 o'clock, and decided to pull the switch, even though it was checking good through it with the meter, there is no way I would have found the broken wire terminal hidden inside the insulating sleeve.

As many problems as somehing like a relatively 'simple' electrical problem like this, on a 14 year old machine without any electronics, really makes me think. I can't help but feel sorry for the poor guy, with the lastest and greatest piece of electronic machinery, when it comes to a screaching halt, in the middle of the field, with an 'electrical issue', at the worst possible time. Just think, 30, 40, or more, (or in this case only 14) years ago when a machine broke it was just a matter of tracing the dozen or so wires needed to make it operate to figure out what the problem was. Yes there was always the chance of something like a broken terminal, or something else odd and hard to find happening, but but basically it was all wires and switches, not circuit boards. Usually you could even bypass a problem to get the machine going until it could be properly repaired when it's work was done. Nowdays it has to be the factory part/computer, which is probably going to be a special order, nonreturnable (even if it turns out not to be the actual problem) item. Funny thing all of the electronic/computer technology that is supposed to provide so much cost savings for the owner winds up costing him almost as much, if not more, in parts, down time, and mechanics hourly charges when something goes wrong, than an older machine, that he could at least do a work around on himself, ever would.

Sorry, didn't mean for this to turn into an 'anti-technology' rant but days like today make me realize that as big of a PITA as any electrical problem can be, when you throw in the electronics it can be a true PITA and NIGHTMARE,to say the least...but equipment treads further and further into that whole nightmare with every new generation.......Funny the lastest issue of an engineering magazine I get has an article written by an engineer, who's son is also an engineer, basically saying that far too many machines nowdays are being over engineered with far to many features for the averageconsumer to ever figure out. Like he was saying, if his and his son's engineering degrees, and advanced education, weren't sufficient to help them figure out all of the technology in the average car, then things had to have gone way to far. So, for you guys with the latest and greatest, good luck..........

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08-14-2012 20:02:32

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 Re: Electrical Troubleshooting in reply to NCWayne, 08-13-2012 22:53:22  
Back when I was turning wrenches on combines the single biggest cause of downtime was electrical by far. A $300,000 dollar machine sat still because one fuction wouldn't operate because the wire to the solenoid in the hyd valve was dead because one of several murphy switches might be bad, but which one is it? Is it a backed out pin in a 64 pin plug? Maybe the switch under the seat isn't working. Nope! How about the aftercooler overheat switch. Nope, And on and on it goes. Jim

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08-14-2012 19:06:15

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 Re: Electrical Troubleshooting in reply to NCWayne, 08-13-2012 22:53:22  
had the gauge panel to suddenly quit on one of our trucks,mechanic that is good with electronic problems spent the better part of a day trying to locate the problem only thing he could find kept referring to the data link cable which was ok dealer said it was a component that cost 400 dollars and they had to program it,so we carried to the dealer two days latter they called and said it was repaired, bill was 1500 dollars and the problem was get this, was an ecm that controlled the AIR SYSTEM on the truck was malfunctioning causing all the trouble, my question to them what was wrong with the manual controls that for years worked fine,three days lost usage plus repairs over modern technology that wasn't needed in the first place

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08-14-2012 06:54:21

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 Re: Electrical Troubleshooting in reply to NCWayne, 08-13-2012 22:53:22  
New tractors, combines, planters are just a 3 or 5 year lease deal, no one can afford to own one of those rigs past warrenty any more. The electrical on them is just nuts.


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Billy Shafer

08-14-2012 05:53:44

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 Re: Electrical Troubleshooting in reply to NCWayne, 08-13-2012 22:53:22  
I had a BFA Onan that was driving me nuts. Would crank and run just fine. But would at times shutdown or act up. After two days of looking. I laid my hand on one wire. The wire bent more than it should have. Checked it out. Found wire broken on the inside but was fine on the outside cover.

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08-14-2012 04:54:34

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 Re: Electrical Troubleshooting in reply to SweetFeet, 08-13-2012 22:53:22  
Ought to scare the crap out of us to get on a plane with hundreds of miles of wire & thousands of connections & millions of transistor junctions and head across thousands of miles of ocean....we must be crazy! :wink:

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08-14-2012 07:16:20

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 Re: Electrical Troubleshooting in reply to JMOR, 08-14-2012 04:54:34  
Planes, cars with 'fly by wire' controls, etc, etc.......they all scare me to a degree. The problem though is not so much the technology, as it is the 'hands' it's being put into, and the time spend maintaining it. Think about it, a plane is required to have certain checks, both electronic and mechanical, at set intervals to insure things are working properly. Too planes usually have redundant systems on critical functions. Cars and equipment don't typically have those things.

Heck, back up from the electronic side of things and think about something a bit simpler when it comes to 'new' car design. On the older vehicles using V belts you could lose your alternator belt and still drive until the battery died. If you lost the power steering belt you just drove manually until you could get to the next exit and find another. Same with the A/C belt. Now if you caught the lost belt in time it could be temporarily replaced with a piece of rope, twisted nylons, etc, etc as an emergency repair until you could get a new one. With the serpintene belts being used on newer vehicles, when it goes, EVERYTHING goes, and it has to be replaced with the identical belt if you plan to go anywhere. Then there is the whole case of having to engineer water pumps rotating in reverse for engines that origionally had V belts to be converted to serpintene drive, etc, etc, etc. In other words something simple and easy, like a V belt, was reingineered into something not so simple and easy. The result was nothing but alot more parts needing to be manufactured and kept on hand, and a consumer base that is now expected to actually maintain their vehicles and have belts changed before they break so they don't get left stranded.

The same holds true for all of the electronics. Properly maintained and used in the 'proper' places, everything has it's place. The problem is electronics are now being used in places that have always been problematic for them, and they have no business being used there....but still are in the name of 'comsumer demand'. Basically the average consumer has driving technology to the point that it is not longer as good for them as they had hoped it would be, and as the advertisers tell them it continues to be. So, they fuss, cuss, and then go right out and buy the latest and greatest electronic gadget for twice the price the same old, non-electronic item would be and the cycle continues.

Be it plane, car, or not being able to find anyone locally with a plain old spring type, non-electronic fish scale in the end, YES, the whole mentality scares me......

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John T

08-14-2012 04:45:50

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 Re: Electrical Troubleshooting in reply to NCWayne, 08-13-2012 22:53:22  
Wayne, another thing many gents (you know, Billy Bob and his beer guzzling know it all brother in law I'm always referring to lol) miss when troubleshooting with a volt meter or a test lamp is they think all is fine as voltage is present as indicated by the meter or lamp butttttttttt thats an extreme low current test anddddddddd when an actual high amperage load is applied, thats when things fail due to voltage drop across a high resistance.

John T

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08-14-2012 08:00:24

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 Re: Electrical Troubleshooting in reply to John T, 08-14-2012 04:45:50  
Your right. The problem is things that could possibly be tested in a lab type situation aren't always possible to test in the field where all you've got is a meter or test light. Too when you don't have any idea what the current draw on solenoid A should be, what resistance is supposed to be on resistor B, and there is nothing you can do to find out because the factory doesn't release that information, even in the service manual (if your lucky enough to have on). At that point I don't care wether your Billy Bob or his beer gussling cousin, the multimeter is all there is and all you can do is rely on what it tells you.

Cases in point. About ten years ago I had an engine that wouldn't start because the solenoid in the fuel pump wouldn't pull in. Based on both my multimeter and a test light I had 24 volts to it, but it still wasn't working. This left me no choice but to pull the pump and take it to a repair shop. Put it back in and it still didn't work even though voltage was still resent. Tracing the wore back I finally found a connection where all but one strand of a 14 ga wire had broken off from a terminal end. Like you said, the one strand was carrying enough current through it to light a light, and read on the meter, but not enough to pull in the solenoid. In that case testing with a multimeter was pretty much all you could do. There were no specs on the current the solenoid should draw to know wether it was good or not so pulling the pump to have it bench tested and repaired was the only option.

Taking things a step further. Several years back I was talking to a dealership mechanic about some problems with a newer machine. He had just came back from a week plus working on a brand new machine that the customer had only had for a few days before it starting having trouble. Given the newness, and large size of the machine, it wasn't something that the factory could just swap out as a lemon. As a result when the mechanic wouldn't get it fixed on his own after several days, they had sent a team of their engineers down to help out with the repair. After nearly a full week of testing, tracing, etc, etc, etc they had finally come to the conclusion that there was no fixing it and had resigned themselves to having to give the customer a new machine. That was about the time one of the engineers disconnected a connector and noticed that when he hooked it back up it didn't feel quite right. Turns out one of the pins in the connector wasn't engaging with it's mating half in the other side of the connector. Instead was riding down beside it making partial/intermittent contact. A new connector body was installed which fixed the problem with the pin not lining up, and the machine was repaired. Thing is this pin was for a ground leg, which made it impossible to find given the testing proceedures the factory provided for the machine. That being the case they could have tested for a year using the factory guide, factory test tools, etc, etc and still not found the problem. So, here you have a problem that, even with a factory guide, factory engineers, factory tools, etc it still couldn't be 'tested out' and nothing but 'dumb luck' solved the problem.

In another instance I read about in a trade publication a crane stopped with it's load hanging over a traffic lane while working on a bridge. The interstate had been closed temporarily for the pick, but then had to remain closed until the factory tech was flown in to troubleshoot and repair it. As you can imagine this cost the contractor BIG BUCKS. In the end what had happened was the operation of the machine had caused coffee to slosh out of the operators cup and it found it's way into what was supposed to be a sealed housing and screwed up a circuit board. In this case the tech was able to troubleshoot the problem and solve it relatively easily according to the article. My point here though is here is a case of technology causing BIG problems, and a BIG expense for a company, all over an operator doing what millions of them do, drinking coffee at work.

In cases like these having a degree in electronics, having 30,000 worth of equipment, and even having the factory manuals, is all great. In the end, all of that matters only a little bit as troubleshooting problems on new machines like these is really nothing but a crap shoot where you hope to get lucky and figure out what's going on.....And hope that by replacing harness A, B, or C, the three options the manual gives to repair the suspected problem, will actually repair it. Thing is hanress A, B, and C are $2500 worth of nonrefundable, special order parts that comprises 90% of the machines complete wiring harness, and take a weeks worth of work to change out.....Just so the throttle works correctly.......

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dennis min

08-14-2012 07:10:19

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 Re: Electrical Troubleshooting in reply to John T, 08-14-2012 04:45:50  
John T,



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dennis min

08-14-2012 00:27:57

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 Re: Electrical Troubleshooting in reply to NCWayne, 08-13-2012 22:53:22  

I too had a small issue electrically related of course. After many hours of digging around, one of the pins of a multi-pin connector was corroded, but just enough to read voltage on a high input impedance multi-meter, but not enough to run the pump.

Of course the relays and ECU were suspect, thankfully that was not the case.


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