Cat 314C LCR Not charging

1. #1Nige2025-09-04 13:09

   I can supply the schematic. Check your message inbox. Hopefully other can chime in with more suggestions.

2. #2SWoods2025-09-04 23:45

   Sorry title should be CAT 314C not 3414C. Nige, Thank you for the schematic.

3. #30072025-09-05 07:22

   Hello Swoods, Nige sent me the schematic and i had a quick look. Firstly i am concerned when you say 22.7V, so are the battery's also dropping to that voltage when running or do you have a 3V loss down stream of that 60A breaker and the alternator??. The wiring diagram shows two green and a yellow wire no black? So the single green you measured is probably (K776-GN-18 Green) and is the star point of the stator and it goes to the starter interlock relay and the hours run meter. When the alternator is excited and charging it produces a very lumpy 12V DC voltage that your multi meter may not read well. If you hour meter is not ticking over when running then your 7.2V is not enough. You can double check that voltage up there also if it is easy to get to. The fact that you have 7.2V is puzzling because if the alternator is not excited there should be nothing on that wire. If the engine was idling slowly might explain the low voltage but still the voltage on your output terminal should rise so appears like a faulty alternator. (Lets hope not) The other two wires are (309- GY-18 Grey) is ignition 24V. Going from memory here and having a guess but the other wire (403-GN-18 Green) i think gets power from the starter interlock relay also but the power circuit that is providing power to that relay comes through a plug in diode near the starter relay (330-YL-18) near the starter relay. All of those diodes are troublesome and i read people on this forum having to replace them regularly. So I would check those first if you do not have power on that second Green wire. Instead of struggling at the back of alternator see if you peel the loom open near the alternator and pierce the other two wires with very thin sewing needles to test with your meter. You can always tape up the small wound in the loom. If you can establish what voltages you have there as a start in the process. Hope this helps.

4. #4SWoods2025-09-05 22:47

   Thanks for the info, hope to get back to TS. To make things easier, I did get the chance to remove the counterweight thanks to an excavator that tracked over from working at a neighbor. Thanks again for all the info.

5. #5SWoods2025-09-30 01:31

   Sorry for the delayed Update on CAT 314C electrical not charging. With the help of a mechanic, did a lot of T/S, continuity checks, and parts replacements and sill not electrically charging batteries when running. Continuity checks ok to each wire at Alternator (K776-GN, 309-GY, 403-GN, 109-RD, and 200-BK grounds) to Conn #6 and beyond into Start Control Relay, Diodes, Heater Control Relay, service meter, etc. No open circuits were found. Grounds checked out good but still cleaned and reassembled with dielectric grease. Replaced the following components: Cat new Alternator (not a Re-man), 3- Diodes, Start Control Relay, Heater control unit. With engine running, Alternator “p” wire 403-GN shows 14.5v. Battery light on dash monitor is off, service meter is ticking, Alternator not charging Batteries. If wire 403-GN is pulled off the Alt terminal, the Alt charges. Wire 330-YL Start Cont Relay at the monitor reads 14.5v. What is the function Theory of Operation of the Start Cont Relay? What is the actual function of the “p” wire 403-GN attached to the alternator? Anyone see this type of problem before? Any help on where to go next would be appreciated. Thanks

6. #6Nige2025-09-30 06:34

   403-GN usually provides the signal for the hourmeter and for the tachometer if one is fitted.

7. #7SWoods2025-09-30 09:45

   The 403-GN in my machine and schematic shows it at the single wire "p" at Alt to the Start Cont Relay and splits off to Conn #2 for Attachment Product Link (which is capped off). The 2-wire plug (K776-GN & 309-GY) at the Alt has the K776-GN going to the Start Cont Relay and also splits off to feed the hour meter. 309-GY comes in from the 5amp fuse on the fuse panel. The weird thing is that when the system initially stopped charging the batteries and the unit stopped running, the console Batt indicator light never illuminated. It always illuminated when the key is on but goes out once the engine is running even though batteries are not charging. That currently remains the same after all of the component replacements. If I disconnect the single "p" wire 403-GN from the Alt when running, the Alt charges but the console Batt light is illuminated. I'm not an electrical guy, but this really does not make any sense to me. Anyone have any ideas?

8. #80072025-09-30 11:16

   You have a tough one to crack and does not make much sense to be honest. It is very unusual to have a wire go open circuit and the alternator then excites. If you had an old alternator there and pulled it apart and posted some pics of where the wires were going to inside i could tell you straight away what it does. There seems to be so many variants out there its hard to tell exactly what the terminals are. As best i can tell P is Tacho L is Lamp and R is ignition. The ignition R is straight forward and makes sense that P is tacho because it goes to Product Link which has Plus,Minus, Tahco, two twisted pair Coms wires. But L does not have to be Lamp because the console controls the lamp and normally looks at Star point in the windings That all sounds straight forward but its not because the tacho circuit can be wired in a few ways and an alternator with ignition on it can have the lamp circuit wired a few ways internally as well. The function of the starter inhibit relay is to inhibit the starter from being engaged if the engine is running. Normally they just use the lamp circuit to infer if the alternator is charging, the engine must be running. You seem to have Lamp and Tahco circuits going up to that relay which i have not seen before. Some times they kill the field circuit in the alt when the ignition is turned off so the Alt dose not keep powering every thing with the key off. Sometimes just turn the ignition off on the alternator. Your inhibit relay has all those circuits there and can be doing ether when the ignition is turned off that relay. You used to regularly see the alternator been inhibited and that circuit also going through a small set of contacts in the battery isolation switch, if someone opened that switch it would stop the alternator because it would be isolated from the battery's. That is not shown on yours. Just guessing that if your light is now not working with P off the alt that 403 wire is being used to determine if the engine is running. That would mean that the K776 L wire is what they call (Sense) wire and maybe they are turning that on and off to control the alt. You could go back to basics and pull P wire off the alt and check what voltages you have on L and R with the ignition on and motor not running. Up at that relay K776 or 403 wire is turning your battery light on and off in the consol. You can start documenting which wire does what because the console can use ether one of those wires for that function . You can check if the starter solenoid is being inhibited when the engine is running and which of those wires are being used for that on the starter inhibit relay. Pull the solenoid wire off the starter and use a lamp or meter there so as not to engage the starter. It would be a start to determine if it is on the alternator side or machine side. If its starting some of it must be working ok because when you turn the key to start the power to engage the starter goes through the neutral relay, through the start relay, up through the bottom diode then up to the start inhibit relay and finds it way to ground in that relay. But does that inhibit relay go open circuit when the engine is running??

9. #9SWoods2025-10-06 02:12

   2004 CAT 314C Excavator Update on Electrical Alternator Charging System Testing 10/3/2025​ Testing performed with various Alternator wires disconnected / connected. Summary of results below, see attached excel chart for specific data. Test #1 Alternator “P” single wire 403-GN Disconnected, all other wires connected. When running it is charging but Dash Battery light is On constant. Test #2 Alternator 2-wire plug (K766-GN & 309-GY) disconnected, all other wires connected. Hour meter is On constant with key regardless of engine running or not. System Not charging when running. Test #3 All 3 control wires to Alternator (403-GN, K766-GN, 309-GY) disconnected. Dash Battery Light and Hour Meter constantly On with key regardless of engine running or not. System charging when running. Test #4 All 3 control wires to Alternator (403-GN, K766-GN, 309-GY) Connected. With key on the dash battery light is on and hour meter is off, when running the dash battery light is off and hour meter is on. Noticed system voltage system decreasing to approx. 19v the increase to system charging. Test #5 & 6 Recorded voltage changes with time. Upon engine running, voltage would decrease over 2-3 minutes to approx. 19v then start increasing to full charge voltage to approx. 28v. Test was repeated with same results. Conclusion, system appears to be charging after 2-3 minutes of running. Some of the components that were replaced may have fixed the charging problem and I missed it by taking reading’s immediately upon running? Questions: Is this part of a normal system operation for the charging system to decrease in voltage upon start to a low of approx. 19v then ramping up to a full charging system? Is there a timer that controls this function? If this is not normal, is there a bad component or timer somewhere in the system? Thanks, Steve

10. #100072025-10-06 07:32

    Hi Steve, The P wire is what they call star point in your alternator windings and in your case it is what the start inhibit relay uses to determine the alt is running and it turns the light off. When the alternator is at rest there is no voltage and when the alternator is running the P terminal will have exactly half the output voltage. L is the lamp and R is ignition. From what i can see the alternator at least is perfect and in test 3 it even self excited with no wires on it. The only reason the light was on because the p wire was off and did not tell the start inhibit relay to turn the light off. An auto electrician would have an amp meter on the alternator output which would be a great help. What is screaming at me is the voltages you are reading. You started this thread saying you checked all the earths with a lamp. I think you have to revisit all those connections with a multi meter with the engine running if possible. You never answered me when i asked about the 3V loss between the alt and batt (would have expected .5V at most). Where are all your tests negative reference from the engine block, chassis or neg terminal on the battery? The negative has to make its way through the isolator over to the chassis and then the engine block and any connection that is loose or dirty and starts to vibrate with the engine running can be a likely place to start looking. In answer to your question no alternator to my knowledge has slow start or ramping system. Not sure where your ground reference is in test 4 but there is clearly an issue of bad connection or earthing issue. Even if the belt was slipping on the pulley the output voltage would only come down to the terminal voltage of the battery. The R wire controls the output voltage of your alternator but you are showing the output terminal going below batt voltage which is not possible without a bad connection. In test 4 unless you have all your lights on and every thing under the sun turned on i would have thought the the battery terminal voltage dropping 4.46 volts was on the high side. Interesting to know the current draw. The absolute kicker is test 4 where B+ terminal on the alternator is going below battery voltage when there should be a large wire and breaker going straight to a large multi terminal block and then the battery. Please explain? Be aware some circuit breaker can arc and burn on there contacts for a while till they weld them selves together which would give the illusion of what you have there. I modified slightly the attached picture to give a basic picture of what you have.

11. #11Simon C2025-10-06 16:49

    You never answered me when i asked about the 3V loss between the alt and batt (would have expected .5V at most). I totally agree with you after reading this thing over twice, need to do proper voltage drop testing of Alternator output post to Battery Positive, and Alternator housing to battery negative for voltage drop. Any high readings is totally indicative of a bad connection of some type. 0.5 Volt DC from one end to other would mean a problem on the ground side. A guy can quickly install a jumper cable from negative at the battery to negative frame on alternator and see what changes. Did this recently on vehicle of customer to prove the ground side was junk. Can easily be done on positive output of alternator to battery positive (24 volt post ) to see what changes. Some fast and inexpensive troubleshooting tricks. Simon C