Need help with Onan Marquis Gold 5.5k

[Dantie]

Thanks in advance for any help gentlemen. I have a 2005 Holiday Rambler Vacationer 37 by Monaco. It's new to me and I've learned a lot but this problem has me perplexed. It has an Onan Marquis Gold 5.5kw genset. After some tune ups a new control board and a new carb, the unit was running great! Every two weeks I would crank it and run it for 30 minutes to keep it running smooth. Every time, it cranked super smooth. Came back to it after two weeks and no matter if I press "prime" or "start" on the rocker switch...all it does is prime! Batteries are new, connections are secure and clean. 13.6v at batteries and at the power lug on the unit. Isolated the coach switch, no change. Isolated the switch on the genset, no change. All the rocker switch dies is prime. As I said, control board is 8 months old. Unit is plugged to shore power with a 50amp power management system/surgery protector on it. Tried starting genset with shore power on and off, no difference. Disconnected power lug for an hour, no change when reconnected. For the two week time interval, the unit was on shore power and nobody messed with it! What could cause the switch to behave this way? Any help is appreciated guys, I'm stumped.
Don

[SteveJ.]

Sounds like it's time to dig out the multi meter, or a credit card, or load the parts cannon.

You will have to do some investigating to narrow down the cause, or see above.

If you do not have the repair manual they seem to be available all over the internet.

[followingsea]

Originally Posted by SteveJ.

Sounds like it's time to dig out the multi meter, or a credit card, or load the parts cannon.

You will have to do some investigating to narrow down the cause, or see above.

If you do not have the repair manual they seem to be available all over the internet.

What Steve said!

My Onan is propane so switch is different. First do not assume that replace a part recently means it is still good. The part failure could have a cause that is not corrected.

Check fuses, breakers, and connectors. This does not cost anything.

Since I have had two vintage Onan, I have a spare portable generator.

[donr103]

So when you press starter button on generator.. does the engine even crank? Basic tests I would do.. 1st check for bad ground.. I would take jumper cables and one end on beefy part of gen eng.. next one on frame ground.. really grind it on there to make good contact.. you are doing fast check for ground. Then try.. if that works you got bad ground.. if not..

If still problem.. expose the starter relay under control board.. I would use any heavy gauge wire.. to reach in there and touch to one side of starter relay to the other.. it's too tight in there to use jumper cables.. but you are looking for big spark or to hear starter engage.. see if cranks .. you are checking starter relay..

Now many members post here.. the harness on control board can not make good contact... so you need to closely inspect each wire and pin on control board.. the plug on harness can vibrate loose.. some have to use zip ties to hold it on..
Critters love old rv and eat, short, and build nest in worst places.. so when things go haywire and don't make sense then keep critters in the back of your mind all the time report back on test.. better opinions will follow
Good luck and keep us posted

[AimHigh]

I had something similar with a different switch and after troubleshooting the circuit, it ended up being a faulty switch. The momentary toggle switches sometimes fail in one of the 2 positions (usually the one that gets used the most). Take a multimeter to the contacts of the switch to verify functions and you can also jumper the switch to start the generator. I use a Power Probe for troubleshooting all of my DC circuits and you can use it to apply power or ground whichever is needed. It's one of the best tools for Motorhome owners to have and with the extension that comes with it I can reach anywhere on our 40' bus. Good luck.

Jerry