I believe that you are describing a situation where the Onan attempts to turnover, but it seems as though you are trying to start it with a weak or dead battery. I recently reviewed this situation with a client. I think this may help, if not solve the issue:
On all of the SMs and 54s that I have checked, the length of battery cable to the Onan is almost twice as long as the cable to main engine, but the size of the wire to the Onan is the same size (gauge) as the main engine. Logic tells me that either the main engine battery cable is oversized, or the Onan cable is undersized.
The Onan has starter battery connection terminals on the left-side-facing and near the rear of the Onan. The Onan has a hidden-from-view cables from the battery connection terminals mentioned above to the battery side of the negative solenoid and positive starter solenoid. This is Onan Part Number: 338-3577-01 Battery Harness.
I believe, that in at least some cases, this
Part Number 338-3577-01 Battery Harness is the cause of a loss of amperage throughput to the starter. I have advised a few clients when experiencing this issue to:
If all of the above is checked/completed and the Onan is still not starting, You should shut off Battery Main Switches to perform the following:
- Ensure that the starting battery is in good condition
- The battery wire terminal blocks in the first sentence above are clean and treated with CorrosionX
- The negative solenoid is working correctly
- And that all starting circuit and battery connections are clean and treated with CorrosionX
IMPORTANT TO ALL: If you cannot identify the components I have identified and/or you are not competent with DC voltage and wiring, seek professional help to do this.
- Fabricate a jumper wire using appropriate sized copper wire and ring terminals (probably at least 8mm diameter (AWG-1)) from the negative connection block on the outside of the Onan (mentioned above) to the battery-side of the negative solenoid.
- If this does not work, next fabricate a jumper for the positive side.
Alan, I know that you are competent. Please let me know if this works for you and I would appreciate photos. I have tried to find a drawing of the suspected connection wire, but have not. There is limited evidence that points to this jumper wire being a solution, but I am not positive.
CW Bill Rouse
Yacht School - Supporting Amel Ownerswww.YachtSchool.us
720 Winnie St
Galveston Island, TX 77550