Dear Dave,
I’m having trouble with the battery disconnect switch energizing/de-energizing the solenoid. It’s hard to trace wiring for hidden fuses/breakers. HELP. —David G., 2015 Thor Four Winds 31W
Dear David,
Typically, the battery disconnect switch on a motorized RV is controlled by a solenoid located near the battery compartment. You will see a heavy-gauge cable coming into the solenoid and another going out. This cable is usually the same size as the positive cable connected to the house battery—typically 6-gauge.
Rocker switch
Your Four Winds Class C should have an on/off rocker switch located either on the cabinet near the entrance steps or on the dash. That switch is wired to the solenoid and creates an “open” circuit—similar to physically removing the positive cable from the battery.
Unfortunately, Thor Motor Coach does not provide very detailed wiring diagrams for some older units, as we discovered while working on a 2016 Thor Challenger. However, the setup is similar to what Winnebago Industries used during that same time period, with a rocker switch controlling a battery disconnect solenoid.
Battery disconnect
Here is a screenshot of the 3D drawing available on the Winnebago site that shows the battery disconnect and the switch.
If the battery has sufficient charge, you should hear a noticeable “thump” or “clunk” from the solenoid when it engages or disengages.
I’m not certain of the exact state of charge (SOC) required for operation, but it would likely need to be above 50% SOC. Keep in mind that 50% SOC on a 12-volt battery is not 6 volts—it’s closer to approximately 12.1 volts at rest. Here is an SOC chart.
When inspecting the battery compartment, follow the red (positive) cables and look for a solenoid mounted nearby. On the 2016 Thor Challenger we worked on for RV Lifestyle & Repair, the solenoid was mounted just above the batteries.
It can be difficult to see due to the cluster of wires and cables, but it will have the heavy positive cables attached to it. Here is a photo of that compartment and an arrow to the solenoid.
I am not aware of any specific circuit breakers or fuses directly tied to this disconnect solenoid or switch, although that can vary by model.
To troubleshoot
- Use a multimeter to verify you have 12-volt power at the battery.
- If the battery is below 50% SOC, plug the RV into shore power. The converter should supply approximately 13.6 volts.
- Verify DC power is reaching the solenoid.
- Operate the rocker switch and listen for the “clunk”.
- Check for DC power coming out of the solenoid when engaged.
If there is no output power, the issue could be either the rocker switch or the solenoid itself.
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Dave Solberg is a leading expert in the RV industry and the author of the “RV Handbook.”
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