How to Locate Your Intellitec BD-0 Disconnect Switch Latching Relay in Your RV

The Rundown

On your 2005 Ford E450 Isata 250SL, the latching relay for your Intellitec BD-0 Disconnect Switch is typically located in the main 12V fuse/relay panel, which is usually mounted inside a compartment on the driver's side exterior or sometimes in the battery compartment area. Since you're specifically looking for the relay to check its fuses, you'll want to look for a larger rectangular relay (about 2" x 3") that's different from the standard automotive relays - it will be labeled as the "Battery Disconnect" or "BD Relay" on the panel cover or nearby wiring diagram.

The Intellitec BD-0 system uses a latching relay that maintains its position even when power is removed, which is why it can disconnect your coach batteries and stay disconnected. This relay is protected by external fuses in the circuit (see manufacturer specifications for amp rating) that can blow if there's a surge or short circuit. On Dynamax coaches like your Isata, this relay panel is most commonly found in the front driver's side compartment, behind a hinged or removable cover, though locations may vary by specific RV model.

Why It Happens

The circuit fuses protecting the latching relay blow as a protection mechanism when there's excessive current draw or a short circuit in the 12V coach system. Common causes include appliances like inverters, refrigerators on 12V mode, or water pumps that develop internal shorts or when wiring gets damaged from road vibration or rodent activity. The BD-0 system is designed to protect your coach batteries from completely draining, but the relay's internal fuses protect the relay itself and the main electrical system.

Other common causes include connecting jumper cables incorrectly or having a failing converter that sends too much voltage back through the system. Age is also a factor - after 18+ years, the relay contacts can develop resistance that causes heat buildup and eventual fuse failure. Sometimes the relay location isn't obvious because it may have been relocated during manufacturing or service, especially in smaller coaches where space is at a premium.

Gather These Items

• Multimeter or test light for checking relay function
• Flashlight or headlamp for working in compartments
• Small mirror to see labels on hard-to-reach panels
• Camera or phone to document wiring before disconnecting
• Replacement latching relay (correct part for your model - verify with dealer, approximately $45-65)
• Basic hand tools (screwdrivers, wire strippers if needed)
• Contact cleaner spray for cleaning relay connections
• Wire brush or fine sandpaper for cleaning corroded terminals

The Fix

WARNING: Always disconnect the negative battery terminal before working on any electrical components to prevent accidental shorts, sparks, or injury. Always ensure power is disconnected before handling electrical components to prevent accidental shorts or injury.

Start by checking the obvious locations: open all exterior compartments on the driver's side and look for a rectangular panel with multiple fuses and relays. The latching relay will be noticeably larger than standard automotive relays and may have a clear or colored plastic cover showing the internal components. If you can't find it there, check inside the coach near the main electrical panel - sometimes it's mounted on the back side of the main breaker panel or in a separate enclosure nearby.

Once you locate the relay, first verify it's a plug-in type (not hardwired). If it's plug-in, carefully remove it by grasping the sides and pulling straight up - don't rock it side to side as this can damage the socket pins. Check the external fuses in the circuit that protect the relay system using your multimeter to test continuity, or visually inspect them for blown elements (dark or melted appearance).

If the relay location still eludes you, trace the wiring from your BD-0 switch panel back toward the battery area. The switch panel will have a control wire (usually small gauge, 18 AWG) that leads to the relay location. You can also check your owner's manual or contact Dynamax customer service at 1-800-813-6008 - they keep records of electrical system layouts for older models and can tell you the exact location for your specific unit.

Before installing a replacement relay, clean all the socket terminals with contact cleaner and ensure they're making good contact. Test the system by turning the BD-0 switch on and off several times to verify the relay is latching and releasing properly. The coach batteries should show full voltage when connected and zero voltage at the coach fuse panel when disconnected.

Know Your Limits

While locating and replacing the latching relay is generally a straightforward DIY task, be extremely careful when working around the coach battery systems - these can deliver hundreds of amps in a short circuit situation. Always disconnect the negative battery terminal before removing or installing the relay to prevent accidental shorts or sparks.

If you can't locate the relay after checking all the obvious spots, or if you find multiple blown relays or damaged wiring, this indicates a larger electrical problem that should be diagnosed by a qualified RV technician. The underlying cause of the blown fuses needs to be identified and corrected, or you'll just keep blowing replacement relays. Similarly, if you're not comfortable working with 12V electrical systems or if the wiring appears damaged or modified from original, seek professional help to avoid creating safety hazards or expensive damage to your coach's electrical system.