Saturday, December 9, 2023


Interior lights in RV only work when plugged into shoreline power. Is that normal?

Dear Dave,
My RV’s interior 12v lights work when the motorhome is plugged in to external power and the converter is on. When running off of the battery, they don’t work unless the ignition key is turned to Accessory. Is this normal? We just bought it recently and are trying to learn how to operate things. —Jeffrey, 1986 Itasca

Dear Jeffrey,
Your 1986 Itasca could be either a Class C or Class A motorized RV, as Winnebago Industries did not manufacture a travel trailer at that time. According to the Winnebago website, the only Itasca models were Sunflyer, Windcruiser, and the Phasar, which was a Renault-powered van-styled unit. I would assume you have either a Sunflyer or Windcruiser. I would recommend downloading a copy of the owner’s manual on their website here.

It is a very generic manual covering all the models on both the Winnebago and Itasca lineup, but it does have some helpful information. According to the specifications, the Windcruiser came with two deep cycle house batteries that were located in an exterior compartment on the passenger side of the unit. The Sunflyer had two 90-amp-hour deep cycle batteries standard except for the 22’ and 23’ models, which had only one. A second battery was optional. I was working at Winnebago at that time in the warranty returns department and I believe they were Sears DieHard batteries, but obviously they would be long gone by now!

How the house batteries work

The house battery or batteries provide 12-volt power to the distribution center which has 12-volt automotive fuses and wiring that go to the 12-volt components. Those would be interior lights, roof vents, water pump, and any appliance that runs on LP which also uses 12-volt power to the module board. Both units also had a double-door 3-way refrigerator that ran on 120-volt power, LP, and a 12-volt mode. The 12-volt mode was discontinued just shortly after this model year as it did little more than shutting the unit off and keeping the door closed but drained the batteries in less than half a day!

My suspicion is that your 1986 motorhome, which is 38 years old, is on at least it’s 10th set of house batteries and needs #11! The interior lights are powered by the house battery system.

The first thing I would suggest is to use a multimeter and determine the state of charge. It should be 12.6 volts without being plugged in. Anything lower than 11 volts will not run the lights. I would assume that no other 12-volt component works when not plugged in, such as the roof vents or water pump? When you are plugged into shoreline power, the converter kicks in and provides 12-volt power to charge the battery or batteries, which is why your lights come on when plugged in.

Modern converters provide 13.6 volts if the battery is low and taper off to 13.2 volts for a maintenance charge. However, I do remember the converters in the Elandan and Windcruiser were not powerful enough at times to keep the batteries charged when plugged in if several components were running at the same time. Imaging being plugged into shoreline power and your batteries go dead and the lights don’t work!

Dual momentary switch

Your rig also has a dual momentary switch which is a solenoid that today is called the battery isolation management (BIM) solenoid. It is a connection between the house and engine batteries and charging system. When you are driving down the road, the engine alternator will provide a charge to the house batteries through the solenoid. If your engine battery goes dead due to leaving the radio on or other reason, pressing the “MOM” side of the momentary switch provides a jump from the house batteries to the engine battery. Therefore, when you turn the key on to start the engine, the dual momentary switch is providing power from the engine batteries to the house batteries and your lights come on. The weak link in your system is the house battery or batteries.

One other test you can do is to connect a portable battery charger to the house battery. Without it being plugged into shoreline power, the lights should turn on. Also, you have an on-board generator that will provide power when running. I don’t recall if these units had an automatic transfer switch (ATS) or if you had to physically plug the shoreline cord into a separate outlet called a “J” box.

 You might also enjoy this from Dave 

What are the types of RV house batteries and what do the acronyms stand for?

Dear Dave,
Readers appreciate very much your RV tech wisdom. Could you provide an article on the various battery types available for RVs, those useful for solar power when off-grid and what all the acronyms mean? Thanks. —Colin, 2020 Jayco 26.7

Read Dave’s answer.

Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.



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DAVE (@guest_255784)
2 months ago

Hi Dave I must have missed something (easily done). I didn’t see an answer to Jeffs question to why does he have to have his ignition turned to accessories in order for his 12VDC interior lights to work. Though you give a great explanation of everything else!

Gary Bate (@guest_255803)
2 months ago
Reply to  DAVE

I think that (main) Dave is suggesting that is suggestive that the house batteries are toast? So when the engine battery is on it will also add power to the house circuit which won’t charge up because those batteries are toast? Also I could be completely wrong so…..😂

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