wiring gremlims help

[Welder Dave]

I started my Cat 931B today and noticed the amp gauge wasn't showing a charge. I always check since getting the alternator rebuilt. Then I noticed smoke coming up by the left floor board. Several years ago Bob/Ont suggested I run a new wire from the alt. because it wasn't charging and tracing a break in the wire inside a loom would be frustrating. At the same time I put an inline 30 amp fuse on the wire since it provides all the power up to the dash. The fuse was blown a few weeks ago(don't know why) but I replaced it with a circuit breaker and everything was good.

Today the circuit breaker was hot to the touch and when I shut the machine off with throttle the ammeter was showing a discharge. I pulled the circuit breaker out and turned off the key. Then I started the machine to lift the boom so could I get the side panel off. I also took the floor board out and couldn't find where it was getting hot and smoking. The circuit breaker was cool so I put it back in to see if I could find where it was smoking but now the ammeter was showing a charge like normal. I had 13.26 volts at the battery at about 1/2 throttle which I figured was OK because the battery had a good charge. I ran the machine for awhile with the side cover off and other than taking a little longer than normal for the ammeter to stabilize at 1 tick on the + side everything seemed to work normally and the circuit breaker wasn't hot at all. I thought maybe a ground wire was smoking but I couldn't see anything out of the ordinary. Appreciate any assistance on what could have happened and/or what to check?

 

[Delmer]

I don't know the wiring diagram, this is just some thoughts.

If that was an automatic reset circuit breaker, then it could have been tripped, and heating up the original wiring at the loose/cracked spot in the harness. Of course that doesn't explain what caused the circuit breaker to trip, but if you find one problem, I bet you'll find them both. I'd try to see if you can reproduce the heating by removing the circuit breaker and running some current through that wire (battery charger on the big alternator terminal and lights on with the engine off) then if you don't see anything heat up (using an infrared thermometer/temp gun) then start wiggling the harness to see if you can find the spot.

 

[Welder Dave]

I don't have lights on the machine. It has a 4 in 1 bucket and factory backhoe attachment but no lights! Well there is a dash light. LoL Of course when I saw smoke there was no way to see exactly where it was coming from with the side panel on. I don't have electric power where the machine is but I'm thinking of seeing what voltage it puts out at the alternator compared to what it has at the battery as 13.26 volts seems a little low. The + wire I ran looks good but if a ground wire is the problem maybe would cause a lower voltage reading at the battery?

 

[Delmer]

Again, I'm guessing, you probably only have the battery cable for a ground on that machine? that should make it easy to check. Check the voltage from one end of the cable to the other with the engine running. Or feel it for any breaks, or weak spots. Or heat. That would show up on starting more than charging though...

It's possible for the harness to have an open and a short in the same place, intermittently. Insulation wears out, wire arcs out. look for any rubbing on the harness, in addition to bubbling from the heat.

Yes, 13.2V is low, it's not like it's some modern car, that alternator is probably aiming for closer to 14.5, screw battery life, just make it start.

 

[Welder Dave]

There is a small ground wire at the same connection where I think the engine ground is bolted to the frame but it all seems tight. My thinking is if the heat/smoking damaged a wire it won't let as much current/voltage through. With the engine off I had 12.6 volts at the starter and the battery.

 

[Delmer]

My thinking is if the heat/smoking damaged a wire it won't let as much current/voltage through.

yes, exactly. Battery cables will have acid work it's way up the end and corrode away to nothing. Anywhere a wire flexes can crack the wires and lose connection even though the plastic insulation looks good. Any connection or connector is suspect. Checking things with the current flowing is helpful, you might need to add some loads if the machine is bare bones.

 

[DMiller]

I would at least hand over hand that alternator feed cable. To me sounds like a hard intermittent short.

 

[Welder Dave]

The wire from the alternator up to the circuit breaker at the dash is good. It is higher where it comes through the firewall and isn't where the smoke came from. I did some more checking today and the voltage at the alternator with machine off was 12.75 and 12.7 at the battery. Starting everything seemed normal and the alternator put out 14.12 volts and the battery showed 13.91. These seem like decent voltage for charging. The alternator and battery are at opposite ends of the machine so maybe it's normal to lose .2 volts through the wires? The small ground wire bolted to the frame by the starter didn't have any plastic over the crimp on connector. I wouldn't think Cat would have just a bare connector but I'm wondering if maybe the connection wasn't the best and that's where the smoke came from and the heat made a better connection? I'm just guessing though because everything seems to working properly now. Even the ammeter shows only very slightly on the + side after running for a minute which is how it always used to work. Goes over about half way when starting and comes back showing just slight charging. I'm thinking I should just keep a good eye on the ammeter to see if goes right to zero again indicating a return of the problem. Not sure what else I can do. I think I should to go back to a fuse instead of the circuit breaker though because it will blow instantly and a circuit breaker might take a second or 2. I can get a mechanic friend to take a look but I don't what else I can check? It's like a problem with a car that never shows up when you take it to the repair shop.

 

[DMiller]

.2v is a tad high and you could be correct as to having cooked out corrosion in a ground or another connection. I would start with the ground you noted replace it with a sealed or at last soldered and heat shrinked unit. If the fuse is blowing it is due to excess pressure(amps) in that circuit trying to do what it needs to. Then start looking at battery cable ends and what the cables look like inside, a little swollen region indicates issues internally.

I had one machine years ago fought with a similar issue, ended up replaced the entire ground cable battery to frame to engine block as internal corrosion all the way thru had increased resistance to a level would not crank over with new batteries.

 

[Delmer]

.2V is fine if that was a few seconds after it started. If it was showing just a tad in the + (the battery is charged up and not taking a big charge) then there shouldn't be any voltage drop.

Not much you can do if you don't want to search through the wiring harness. Maybe keep a fire extinguisher on board if there's any junk to burn on the machine.

 

[Welder Dave]

Most of the wiring is inside a loom so it's hard to inspect. I'm going to see if I can get a mechanic friend to help me check some things. I thought it odd the volts were .05 higher at the alternator than the battery with it shut off. I hate trying to figure out electrical problems. Of course it only acted up because I'm taking next week off and want to use it to get some work done. It was showing just a tad on the + side so I agree the battery is fully charged. The day before it was over 1 tick and that's also when the voltage was showing 13.26 at the battery. I'm also don't know if it's common for a circuit breaker to get hot and why did it show a high discharge (1/2 the way over on the - side) when I shut the machine off. The smoke was white and I could spell burnt plastic but where exactly it came from is a mystery. I know the general area but can't pinpoint it. It gets to be where you hate owning equipment because of all the bizarre things that go wrong at the wrong time. If it seems to be working normal, do I run it or do I tear all the wring apart trying to find where it was smoking. Very frustrating!

 

[DMiller]

Circuit breakers only get hot if they are being cycled, that would be indication of some form of short.

 

[Welder Dave]

That's why I think a fuse is better for this application but I'm going to try and check the wiring out better. It may have nothing to do with the alternator but power to the dash comes from the alternator wire. Normally there wouldn't be a fuse or a circuit breaker.

 

[DMiller]

A great deal of older machines used fusable links.

 

[Welder Dave]

There was a fusible link on the starter wire. Machine wouldn't start and by fluke I found power to the wire connection with a test light but nothing past it. I took the wire with the Cat connector to an auto electric shop and they said it was a fusible link because the wire was much more flexible than standard wire.

 

[DMiller]

I am still thinking there is a short somewhere you need to find before it finds you.

 

[Welder Dave]

I'm going to look at it closer to try and find where the smoke came from. I think I may have to cut some of the plastic loom off the wires to see the wires inside.

 

[Welder Dave]

Update on the wiring problem. I friend who's a mechanic came out to take a look today and of course discovered the problem in about 2 minutes. Probably just because he's a mechanic. LoL He giggled the harness (with the machine off) where it goes under the firewall and got a small spark. On closer inspection it was arcing on the bellhousing. He took a harness bracket off and disconnected the wires at the starter so he could pull the harness out enough to look at it. The outside loom at the bottom was hard so he said it must have got pretty hot. He took a knife and cut back the loom and the old wire from the alt. was completely exposed in 2 pieces and 2 other wires in the harness had damage. He thought it was odd everything still worked as it should and the battery was charging. He's going to bring some supplies next weekend and fix it up for me. He thinks I should take the extra wire I put from the alt. off and put it back original.

 

[DMiller]

Don't ever stop til you find the smoker, worked out. And I hate running a new wire around problems as this, if it needs a new wire the problem is still at hand. I had lots of people tell me just to run a new wire as they thought that was a cure all, all it becomes is a birdsnest of more issues, fix it right One time is better in the long run.

 

[Welder Dave]

The only problem before was there was no current coming from the alt. There was no smoke or anything getting hot and everything else worked properly. About 8 years ago Bob/Ont suggested running another wire because it is difficult to trace a wire in the loom. Part of the reason I installed an inline fuse on the new wire. Now with the smoke I've found the problem and can fix it properly. Apparently D3B/931B's are known for wiring problems. They also don't have a master disconnect switch like most other Cats.