Where is fuse/circuit breaker box on Forest River XLR Nitro 31 FQSL. Have power but slide outs don't work. and can't get inside living room/kitchen.

In the link

https://www.google.com/search?q=breaker+box+in+Salem+T27DBUD

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While researching your model, it looks like the panel you need to look for is down right of the bathroom sink. When you open it, keep in mind that the AC & DC circuits are in there. DC has fuse and AC has breakers. Hopefully they are labeled for you to make locating the ones you are looking for easier. Can you pull each fuse to check or is a multimeter to see if you have the 12-13.8VDC on each side of the fuse. Remember there voltage is hot even with shore power disconnected. To remove the voltage, you need to turn off (open) the Main Battery Disconnect. Typically, these are located in the storage compartment area or near the location of the batteries. Just look for a bit red switch or lever. If you find the fuse are good, check your battery voltages. Anything less than 11.8VDC could be your problem. If less, charge the batteries with a trickle charger or put into shore power.

Fuse inside fuse box inside or under tongue re settable fusible link

Forest River manual for your travel trailer says they have hydraulic and electric slides. Look online for the manual for your slide manufacturer for troubleshooting steps.

I've had RV's with fuse/breaker boxes just inside the entry door and my motor home has vehicle fuses under tip up dash, RV fuses (breakers) near floor under fridge.

Contact your local retailer directly or online here: Forest River RV Contact Us Forest River Inc

Contact your local retailer directly or online here: Forest River RV Contact Us Forest River Inc

Hydraulic or electric slide system? If electric, could be a low voltage problem or failed inline circuit breaker. Also, do not try to move more than one slide at a time because it will blow the fuse. If hydraulic, make sure the bypass valves have not been opened. Do not add fluid while the slide are out. If you do, when the slide come back in they will force the excess fluid out of the reservoir and make a huge mess in the storage compartment.

#1 is make sure the RV is FOUR WAY LEVEL before attempting. Check for obstructions at the glide points and also INSIDE the RV. A toy on the floor can stop the slide-in. Those apply whether slider is manual or electric. IF it's electric, first thing to check is the fuse for the slider circuit.