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Ask Dave: New battery, fuses are good, but why don’t lights and switches work?

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. Today he discusses an RV’s 12-volt power system.

Dear Dave,
Something is going on with my 12-volt system. I put in a new battery and power on both sides of the manual circuit breaker and the fuse there is good. All the fuses are good, but the light above the dinette, one overhead, the refrigerator and exterior light along with the two switches by the door are not working. The 110 plug that provides power to the reefer is hot. The two glass fuses in the reefer control box are good. I have the Magnetek 6300A system, which I can hear charging, and the bathroom GFCI is not tripped. What am I missing? Is there a reset on the converter? —Dawn

Dear Dawn,
First, we need to identify what components work on 12-volt power and ones that work on 120 volt. The lights inside and outside run off 12-volt power from the house batteries. The outlets are 120 volt and can be supplied by the distribution center or by an inverter but typically not the GFCI ones. Have you tested the outlet to verify if it has power? If the GFCI trips enough, the outlet can go bad and the button will not pop. I’ve seen that happen when someone plugs one of the small ceramic heaters into either that outlet or one of the others that is connected or “ganged” to it. How did you test the refrigerator outlet? I would start by using a GFCI tester on the outlets to verify power.

What are you testing and what are you using?

What “main circuit breaker and fuse” are you testing and with what type of tester? If this is in the distribution center, it would be 120 volt on the circuit breaker and 12 volt for a fuse. The refrigerator has a circuit breaker dedicated for 120-volt operation. If you are using a non-contact voltage tester, it will pick up stray voltage for over a foot, so you need to use a multimeter with direct contact.

This is a newer distribution center with the circuit breakers at the bottom, the 12-volt fuses at the top, and the converter on the left.

If your rig is older, it could have a unit like in the photo below?

The unit on the left is the actual distribution center with the older model 6300 converter at the bottom. The unit on the right is an upgrade.

Next, let’s look at the refrigerator

Since you indicated the outlet is “hot,” we need to look at the 12-volt supply to the module board. The inside controller needs 12-volt power to run on both LP and 120-volt operations. Have you tried running the refrigerator on LP? If it works, then it’s not a 12-volt issue, but rather something in the 120-volt operation of the module board.

Take a multimeter and check the voltage at the battery, which should be 12.6 volts if you are not connected to shoreline power. 13.2 volts or higher is connected as the Magnatek converter should put out that voltage. If you are plugged in and the voltage is lower than 13.2 volts, there is something wrong with your converter. There are two 30-amp fuses on the converter that help to protect it if there was a short while installing the new battery. If you have 13.2 volts at the batteries, take off the power module cover and check 12-volt power there. You should see the wires coming in and the connection point identified.

Further clarification needed

Does any other 12-volt component work in the rig such as a roof vent, bedroom lights, water pump, etc.? Also, what “switches by the door” are you referring to? If they are switches to the lights that are not working, then that would be related to a 12-volt issue somewhere in the stream.

Does your unit have a larger 2,000-watt inverter? If so, it could be the inverter has “tripped” due to a power loss and needs to be reset or even “jumped.” Some of the older Freedom 2000 inverters would stop working if the batteries went dead and had to be reset with a jumper wire on terminals. If you have an inverter, please provide the make and model and we can dive into it further.

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dale rose
28 days ago

Dave, you commented to try the fridge on LP. I believe that they need 12 volts to open the gas valve, so if there isn’t 12 volts to it, the fridge won’t work on LP.

DAVE TELENKO
28 days ago

Wondering if the salesmans switch is turned off. By the sounds of Dawn’s issues, it really seems like the STORE 12VDC switch is off! Just my 2 cents!
Snoopy

Last edited 28 days ago by DAVE TELENKO
Glen Cowgill
28 days ago

Dave, had that problem once on an older motor home which turned out to be a wire not reinstalled on the positive battery terminal. One of those mistakes that can drive you nuts,