(quoted from post at 19:24:40 11/01/17) I want to thank the members of the John Deere Forum who read my lengthy 24 Volt Explanation. As I said we just scratched the surface of the topic. I want to apologize for the lack of pictures, schematics, and diagrams. My wife is out of town and I do not know how post pictures. My Gathering of the Green Seminars are in color and on Powerpoint thanks to my more skilled wife. The system is much easier to describe with pictures and drawings with arrows to show current flow in various parts of the circuitry.
If you are a tractor lover, the Gathering of the Green is spectacular and the most exciting event I have ever attended. We had roughly 3 thousand attend two years ago. There are some great seminars on painting, hydraulics, carburetion, and all aspects of restoration. Some of the classes such as ignition, starting and charging, painting and carburetion, can apply to all brands of tractors as well as older cars, pickups combines and trucks. Corky Groth's tune-up presentation which is full of information and humor is worth the trip in itself.
I will be teaching seminars on 24 Volts, Distributor Ignition, and another on General Electrical Problems including charging and starting. Once again Thanks for reading!
You are most welcome my friend Tom. I'm glad I, along with others, especially TxJim and Buick (gave an excellent 24 volt seminar at Two Cylinder Expo) and Bob and Dave and ET (I consider as 24 volt experts and the Go To guys on this topic) were able to help you out. Still, its hard for the untrained to understand let alone troubleshoot the system as its a rats nest under the dash and any color coded wires are faded grrrrrrrrrrrr.
Since you were unable to post a wiring diagram, I have attached one for your and the others benefit. Of course this is NOT new generation where a wire could be used to replace use of the iron frame as a return current path HOWEVER the design and theory of the 24 volt system is still similar where the Starter Motor and Generator are two wire isolated off frame (NOT POS GROUND) yet the 12 volt loads like lights and gauges etc are fed 12 volts (as the diagram shows and how they were wired) from EITHER the A or B battery banks, one of which is POSITIVE GROUNDED the other NEGATIVE GROUNDED as shown by the center tie point frame jumper wire discussed below. If you study the diagram you see the loads are balanced as the A feed up to the light switch powers some lights and the other lights are fed off the B feed, one bank of course has its - to frame (NEG Ground) the other its + (POS Ground) to frame.
NOTE THAT JUMPER WIRE WAS THERE FOR A REASON AND SHOULD BE KEPT IN PLACE AND IF YOU EVER HAVE A PROBLEM WHERE SOME 12 VOLT LOADS WORK AND OTHERS DONT CHECK THAT FRAME JUMPER WIRE !!!!!!!!!!!!
OF COURSE as I'm sure you well understand Tom, if two sets of 12 volt lights were wired in series across 24 volts BOTH WOULD WORK FINE even with no frame ground jumper wire and even if in place it wouldn't draw current. HOWEVER if one burned out neither would glow grrrrrrrrrrr yet with the frame ground jumper wire in place as designed and they were built one (A or B fed, Pos or Neg ground battery bank fed) that problem is eliminated. ALSO if a device such as for example a fuel gauge or some sort of relay etc is needed that requires 12 volts IT HAS TO BE FED FROM ONE OR THE OTHER OF THE BATTERY BANKS (The A or B, Pos or Neg grounded) because 24 volts would burn it up grrrrrrrrrrr and where is that 12 volts ????????? Its between one A battery or the other B battery 12 volt feeds (one of which has its POS to frame, the other has its NEG to frame) that run up to the light switch.
BUT REMEMBER the two wire 24 volt isolated off frame ground Starter Motor and Generator DO NOT USE THE FRAME OR NEED THAT CENTER FRAME GROUND JUMPER
ITS ONLYYYYYYYYYYYYYY the 12 volt loads that MAY (may not need if wired in series across 24 volts as can work with NO jumper whatsoever as long as both are conducting) utilize the center frame jumper as the return current path if no 24 volt series path exists) AND ALSO a 12 volt load like a 12 volt gauge or relay etc needs ONLY 12 volts and it has to get 12 volts from either the A or B feeds, one of which is POS grounded the other is NEG grounded as JD diagrams show and how they were wired from the factory. YOU CANT POWER A 12 VOLT LOAD WITH 24 VOLTS and 12 volts is available off the A or B feeds AGAIN sure you can power two equal 12 volt loads off the series 24 volts WITH NO JUMPER REQIIRED AND IT DRAWS NO CURRENT.
EVEN IF YOU SAY ITS OVERSIMPLIFIED I think this is an excellent place to copy and paste the 24 volt portion of the Official John Deere Service Bulletin No 268 as it describes what I just explained above EVEN IF SHORT N SWEET NO ONE SAYS ITS INCORRECT !!!!! and in my years of farming and selling 24 volt JD tractors ITS HOW THEY WERE WIRED !!!!!!! AND ITS HOW THEY WORKED AND CURRENT ALL FLOWED IN THE RIGHT DIRCECTION This is DC NOT AC duhhhhhhhhhh lol
THE electrical system used on John Deere Diesel ( E l e c t r i c Cranking) Tractors is a 24-volt split-load system using 24 volts for the cranking and charging circuits and 12-volt circuits for the lighting and accessory load.
Figure 41A is a schematic draw-ing of the system
A 24-volt generator, controlled by a 24-volt regulator, supplies current to carry the electrical load and charge the four 6-volt batteries connected in series which supply current at 24 volts for cranking the engine. The cranking circuit and the charging circuit are two-wire circuits- the entire circuit is carried through wires and no part of it is grounded to the tractor frame. Two 12-volt circuits are obtained by installing a ground wire between the second and third batteries in the circuit and the tractor frame. Also, the combination switch is in reality two separate switches enclosed in a single housing and operated by a single lever. One of these switches controls current to approximately l/2 of the load, the current being supplied by two of the batteries. The other switch controls current to the remaining 1/2 of the load, current being supplied by the two remaining batteries.
SOOOOOOOOOO THERES WHAT JOHN DEERE HAD TO SAY AND SHOW IN DIAGRAMS SO DONT TAKE MY WORD FOR IT, LOOK AT HOW THEY WERE DESIGNED AND BUILT AND WIRED AND OPERATED FINE AND HOW THAT CENTER FRAME TIE JUMPER WIRE BONDS THE NEG OF ONE BATTERY AND THE POS OF THE OTHER TO FRAME AND HOW A AND B (one Pos Ground other Neg Ground) 12 VOLT FEEDS RUN UP TO THE SWITCH TO POWER LIGHTS AND GAUGES IN AN ATTEMPT TO BALANCE BATTERY LOADS. NOTE a wire could be used instead of the iron frame as the return current path but still its 12 volts off one battery or the other to feed one set of 12 volt lights or the other regardless if wire or the frame serves as the return current path.
CLOSING that's how John Deere describes the 24 volt system and how official John Deere diagrams and publications and Service Bulletins describe the system and how they were shipped from the factory and THAT CENTER JUMPER TIE WAS INSTALLED SO I SUGGEST YALL LEAVE IT IN PLACE EVEN IF ALL WERE PERFECT AND NO LOADS WERE BURNED OPEN SOME DEVICES CAN STILL WORK.
If anyone dislikes the JD system or argue their diagrams or builds were NOT right or its NOT as they (not my words) described above in Service Bulletin and their published diagrams are wrong, take it up and argue with them not meeeeeeee lol
I WANT TO THANK MY FRIEND TOM FOR ALL HIS TIME AND EFFORT I CERTAINLY APPRECIATE IT. In all these discussions we may have bored the others to tears lol but we have learned and benefited from others experience and knowledge and shared and that's whats its all about
GOD BLESS YOU ALL AND TOM AND THANKS FOR YOUR PARTICIPATION AND FOR READING ALL THIS, I sure hope it helped THATS MY GOAL HERE
John T Retired Electrical Engineer