And the next wiring problem: Onan 2.0AJ/R52 Generator.

Started by Mlw, March 23, 2022, 05:31 AM

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1969 D22, 2 x 1974 D24 Indians, 1977 27' Itasca


Well, Unfortunately no luck starting up the generator.

Without a sparkplug I have spark, white blueish so should be OK as an old mechanic at the site is telling me. With the sparkplug... nothing.

So bought a new sparkplug... Nothing.

So as I have bigger fish to fry at the moment with my RV engine the generator will be put on hold. First I'm going to figure out a way to remove the generator out of the RV so I can check it up completely.

to be continued.


Hi Dave,

I secretly was hoping to hear from you  ;). A little off topic: thank you for your excellent website It was a great help answering my questions about my ignition system in my Betsy ans solving my issues with my ignition coil running very hot idling so you could touch it but not hold your hand to it. Now that I've connected everything up the right way the coil feels somewhat warm and you can hold it now.

And now again with the generator, Thank you for confirming my question "Why do I need a momentary switch on the Genny but not with the remote". As said It boggled me, but with you confirming i now will check if the oil switch is there and if so, is the starting technique strong enough to build enough oil pressure to open the oil pressure switch. It very well could be because i allready thought the starter is spinning the engine pretty fast and sparks were there, using the momentary switch or not.

You are also right about the run light. Its connected to a separate connection point which I guess is the charging system of the generator.

I will get back at working on the genny tomorrow and post the outcome here.

warm greetings, Marc.


According to the Parts manual (924-0221) pdf page SUPL-228, the wiring diagram for your unit (2.0AJ-52R) is 610-0199 which is located on pdf page 40 of the service manual (924-0502).  The unit is SHUT DOWN by grounding the points by either the STOP switch, loss of oil pressure switch, or high temp switch.  Given the Oil Pressure switch is normally grounded when no oil pressure is present, in order to START the unit at the gen itself, the momentary switch is used to unground the oil pressure switch during the start cycle.  Based on what I see, there may be no way to have the oil pressure switch installed if you want to connect a remote start/stop switch on the dash.  The motor/generator would have to spin the unit fast enough to provide enough oil pressure to open the oil pressure switch.  I am fairly sure the fancy onan remote stop/start switch with the run light was not intended to be used with this model Onan.  No built in circuit to support the light.  The picture on pdf page 10 (figure 6) of the operators manual (924-0121) is the only one this gen supports by design.

Terminal Board: Pin B+ = 12VDC; Pin 1 = GND; Pin 2 = Shut down Gen; Pin 3 = Start unit

Timing and points adjustment are described in the operators manual (924-0121) pdf page 16.

All the manuals for this are in the members area.
Operators Manual 924-0121
Parts Manual 924-0221
Service Manual 924-0502



 :D :D :D

Thanks man. I will take your advise at heart.

As you can guess my adventures are turning into a blog. If you tell your stories you need to tell the good, the bad and the ugly, I think, and we all know that fixing up an RV more then 40 years old is not exactly a walk in the park.

I guess I would have been a whole lot kinder when I wouldn't have to work in a confined space folding myself in impossible positions to get that very last screw on the back that you can't see out and in.  :angel: :angel: :angel:

Eyez Open

Below is a link to a Onan site. Those guys know there way around those old gen sets. A word to the wise..they also love there toys, be kind with your descriptions.. ;)


So a day later with beautiful weather in the Netherlands I Became a little wiser again. You just need to dive into it.

Looking at another wiring diagram of an Onan it became clear the momentary switch is there to bridge the oil pressure switch and possible other safety features that are there (temp. switch etc. Then there is still the question why you don't need a momentary switch using the remote but that's for later.

I found what the loose wire was for. It was for the choke, but I have to check it because it shorted as soon as I pressed Start because there are no fuses and the wire for the choke is connected directly to the starter solenoid. There is a second wire that goes to a contact point that feeds the light at the remote button telling you your generator is running. and a thick wire for the starter.

My work had some effect because I have spark now. Having no spark was the reason to disassemble the generator. Unfortunately the spark plug is dead as well so still no starting up the generator.

more next week. as tonight my workweek begins again...


Advice in advance: Read this with a big amount of irony  ;)

The Angry message Icon is there again for a reason my friends, so can we PLEASE cleanse this world from people who think they are smart and think they know everything better but actually destroy everything they set their eyes on and are to thick to learn that the end result is going to be nothing but destruction.

SO as the caliper from my passenger side front break still is stuck like the Mount everest and I don't want to pay enormous amounts of import taxes again, I left it soaking in WD-40 again and decided to see If I could finally get my Onan 2.0AJ/R52 to work. Everybody says they are loud but actually very reliable machines and so easy to maintain.

Really? That not everything from the seventees is better was proven swiftly. How, for heavens sake, do you invent a machine that you have to take completely apart just to get to the breaker points. Timing issues? Same thing. Take your generator completely apart, readjust, build it up again, take it apart again when still not right etc.  D:oH! D:oH! D:oH!

That's allready a menace in open air. but what do you think when you can't get your generator out of it's compartment in your RV, because the very brilliant and bright PO decided to build a bicycle Carrier on the back of the RV and welds the beams for it directly in front of the screws to remove the bottom of the generator compartment so you can remove your generator when you need to. It's a good thing there isn't a Nunnery next to the hobby-garage because they would have locked themselves up for weeks if they would have heard me saying what I thought of the PO. 

So with help I spend an entire day figuring out how to remove the genny thru the side door to find it is two hairs too big to fit thru it.  :'(
As I really wasn't looking forward spending a day leaning in a confided space, weeks past until a caliper decided not to cooperate and there really wasn't anything else to do then the Genny. Huge mistake, because now i have a loose wire that i have absolutely no idea of where it came from. I never said I didn't do dumb things myself, but at least I'm asking myself why I'm such an idiot and try not to repeat them.  :-[ :-[ :-[

I haven't found a specific wiring diagram for it but one of a heavier Onan AJ and as far as the specific owner's manual and the wiring diagram is telling me the Brilliant previous owner connected a ground wire to a battery+ connection which probably is the reason my remote control switch from the cabin is not working. Lets hope the idiot didn't fry the circuit.

But I have another problem I don't understand. On top of my Genny there was a heavily corroded switch that fell apart when I tried to loosen it. The following text was on the side.

The manual doesn't say anything about this switch but as far as I understand the text the engine doesn't start unless you hold over this switch. The generator has a start-stop switch which should function the same way as the remote switch in the Cabin, but when you start from the genny you need to hold over this switch but if you start the genny from the cab, you don't need it. The button absolutely boggles me and I just can't understand the use of it other then it would be a safety feature so you will use both hands so that they are out of the way of moving parts?

So I hope somebody will share his wisdom with me and can tell me if the connections of the remote control switch stayed the same over the years. Also the Wiring diagram for this specific generator would be helpful.