Onan produced a control board upgrade kit for those generator sets, part number 300-3950. The kit includes the 300-3763-01control board, a new wiring harness, and some misc. hardware. I don't know how many of these upgrades were made by Onan, but in case you have a generator that has had its control board updated from the 3-Plug style control board (A1),to the 2-plug style, this is for you.
The reason I focus on this particular generator is that it apparently is about the last model to have "points" ignition and I've got one.
When you try to find the correct schematic for your machine, you get pretty close on either side of that changeover,
but never quite right.
If your generator set works fine, you probably don't care about this, but if you try to troubleshoot problems in the control board area and if your generator has been upgraded with the above kit, good luck trying to figure the wiring out. That's because the actual wiring in the control box has been changed a lot. The wires in the kit harness are labeled well as to their destination, but you may well find that NO schematic you find will EXACTLY fit your machine.
That's because Onan kept changing the way they dealt with the fuel pump, and ignition circuits. I even found that, at one time, they got some bad fuel pumps and they changed either the blocking diode arrangement or the series resistor to make up for the problem. Once they changed fuel pump mfr's, its unclear to me if and when they changed the circuit again. You may have a schematic that shows no fuel pump series resistor, when indeed there IS one in your machine.
I recently spent a couple of hours drawing the 300-3950 kit instruction connections onto the schematic 611-1180, which is the
schematic for the 4.0 BGE/F, 6.5NHE/D. This schematic is for the "original" 3-plug A1 control board, 300-3091-02 and it shows
ignition. I was able to reconcile almost all the changes. Once I completed that task, I went looking for a schmatic that would fit
those changes. I selected "611-1206, Rev.A,Modified" as the best fit. It's labeled to be for the BGE/NHE Spec J.
Not perfect, but pretty close.
If you want to make a schematic that is as close as you can get, make these changes to 611-1206:
-S3, the electronic ignition module: Put the points in its place and move C4 to the other side of the coil, the side that connects directly to the points.
-The "Kit" says that R6 (the battery charging wirewound resistor), is NOT connected to J1-3. But, on both schematics, R6 is indeed connected there. If your machine has the kit and doesn't charge the battery, this could be why.
-There may or may not be an "external" fuel pump resistor.
If the above doesn't make sense:
The only way I know to figure out what's really going on in YOUR generator is to get a copy of the Kit instructions and apply the directions to your set.
After some searching, Dennis Risser from Advanced Service And Parts was kind enough to supply me with the instructions, free of charge.
I promised to make my next Onan parts buy from them.
Here's a link to the .pdf: A1 Control Board Upgrade Kit
I am no expert on anything, but I have spent many hours trying to get to the bottom of this particular issue.
Many of the true experts on the Smokstak.com Onan Forum have helped me time and time again.
If this article has been too mystical for you, email me and I will try to answer your questions.