How to Wire Girard Tankless Water Heater: Complete DSI Suburban Replacement Guide

Here's the Deal

SAFETY WARNING: Before starting any electrical work, disconnect your RV's battery and shore power to prevent electrical shock or short circuits. When working around gas appliances, ensure proper ventilation and check for gas leaks using soapy water solution on all gas connections.

You're absolutely right to suspect the DSI system is causing your wiring confusion when upgrading from your Suburban 6-gallon DSI water heater to the Girard II tankless unit. Common causes include DSI (Direct Spark Ignition) systems using a more complex 12V wiring setup than what the Girard II requires, and the existing coach wiring was specifically configured for your old Suburban's dual-mode operation with both gas and electric heating elements.

Your Suburban DSI water heater had multiple 12V circuits - one for the DSI control board, one for the electric heating element relay, and potentially others for status indicators and safety systems. When you removed that unit, you're now looking at a bundle of wires where the main 12V hot feed might not be immediately obvious because it was likely routed through the DSI control module first. The Girard II only needs a single, clean 12V hot feed and ground, which makes identifying the correct wire from your existing harness challenging.

The most common scenario in your situation is that the primary 12V hot wire was actually feeding the DSI control board first, then distributing power to other components. This means you'll need to trace back to find either the main feed wire or identify which wire in your existing harness can provide the clean 12V power your Girard II needs. Don't worry - this is totally solvable with some methodical testing and potentially a small wiring modification.

What's Behind This

DSI water heaters like your old Suburban use a sophisticated control system that manages both gas and electric heating modes automatically. The 12V electrical system in these units serves multiple functions that go way beyond what your new Girard II tankless unit requires. Understanding this difference is key to solving your wiring puzzle.

Your old Suburban DSI system had several 12V circuits working together:

• Main 12V feed to the DSI control board (verify amperage requirements with manufacturer specifications)
• Separate 12V feed for electric heating element relay control (heating element itself operates on 120VAC)
• 12V power for gas valve solenoids and ignition system
• Status and diagnostic LED circuits
• Safety interlock circuits for proper venting and gas pressure
• Temperature sensor power and monitoring circuits

The DSI control board acted as a central hub, receiving the main 12V power and then distributing it to various components based on operating mode and safety conditions. This is why you're having trouble identifying the "main" 12V hot wire - it was all integrated into that control system.

Your new Girard II tankless unit has a much simpler electrical requirement. It needs a single 12V hot feed (typically 8-10 amps), a ground connection, and that's essentially it for basic operation. Some models also include connections for remote temperature controls or status indicators, but the core power requirement is straightforward.

The challenge you're facing is that your coach's 12V system was wired specifically for the DSI setup. The wires you're looking at may include the main feed that went to the DSI board, the heavy-gauge wire that fed the electric heating element, and various control wires. Without the DSI system to act as a distribution point, you need to identify which wire can safely and reliably power your new tankless unit.

Getting Started

Before you start testing wires and making connections, you'll need the right tools and a systematic approach to identify your 12V hot wire safely. Working with 12V systems is generally safe, but you want to avoid creating shorts or damaging your new Girard II unit with incorrect connections.

Essential tools you'll need for this job:

• Digital multimeter capable of reading DC voltage and continuity
• Wire strippers and electrical tape
• Heat shrink tubing or wire nuts for secure connections
• Flashlight or headlamp for working in tight spaces
• Small screwdriver set for accessing junction boxes
• Wire labels or masking tape for marking identified circuits
• Your RV's electrical schematic if available (check owner's manual)

Start by locating all the wires in your water heater compartment and taking photos of the existing setup before you disconnect anything further. If you haven't already removed all the old wiring, document which wires went where on your Suburban unit. This documentation can be invaluable for troubleshooting.

Next, you'll want to identify the main electrical panel or distribution center in your RV. Look for a breaker or fuse labeled "Water Heater," "WH," or something similar. This will help you understand how power was being supplied to your old system. In many RVs, there are actually two separate circuits - one for the 12V DSI controls and another for the 120V electric heating element.

Check your Girard II installation manual for specific electrical requirements. Most Girard II units need 12VDC power - verify voltage range requirements with manufacturer specifications - verify specific current draw requirements with manufacturer specifications as these vary by model. Make sure whatever wire you identify can handle this load safely.

Safety preparation is crucial before you start testing. Turn off the main 12V power to your RV or at minimum, locate and turn off any breakers related to the water heater system. Complete all wire identification and connections with power off, then turn power back on only for final testing.

Making the Repair

Now comes the systematic process of identifying your 12V hot wire and making the proper connections for your Girard II. This process requires patience and methodical testing, but it's definitely something you can handle as a DIY project.

Start by turning on your RV's main 12V power and begin testing the wires in your water heater compartment. Use your multimeter set to DC voltage, with the black probe on a good ground (the RV chassis works well) and the red probe to test each wire. You're looking for a wire that shows approximately 12-14V (depending on your battery charge state and converter status).

Here's the systematic approach to wire identification:

1. Test each wire against ground with your multimeter
2. Any wire showing 12V+ is a potential hot feed
3. Check if the voltage remains stable when you turn lights or other accessories on
4. Look for heavier gauge wires (10-12 AWG) that might have been the main DSI feed
5. Test continuity back to your electrical panel to confirm circuit routing
6. Verify the wire can handle the required amperage by checking its gauge and insulation

Once you've identified your 12V hot wire, you need to prepare it for connection to your Girard II. If the wire has been cut or modified during your old water heater removal, strip about 1/2 inch of insulation from the end. If it has an old connector that won't work with your new unit, you may need to cut it off and prepare a fresh connection.

The Girard II typically comes with a wiring harness that includes the 12V power connections. Connect your identified hot wire to the positive terminal (usually red wire) and find a good ground connection for the negative (usually black wire). The ground can often be connected to a chassis ground point near the water heater compartment, or you may find that one of your existing wires is already a suitable ground connection and already a ground return.

Before making final connections, do a test setup. Connect your 12V hot and ground to the Girard II temporarily (you can use wire nuts for temporary connections) and verify the unit powers on correctly before making permanent connections with appropriate electrical connectors. or small clamps) and test the unit's operation. Follow the Girard II startup procedure in your manual - typically this involves turning on a hot water tap, which should trigger the unit to ignite and begin heating water.

If the unit doesn't respond or behaves erratically, double-check your voltage at the unit terminals with your multimeter. You should see stable 12V+ power. If voltage drops significantly when the unit tries to operate, your wire gauge might be too small or you have a poor connection somewhere in the circuit.

For permanent installation, use proper electrical connections - heat shrink butt connectors work well for joining wires, or you can use the terminal blocks that may have come with your Girard II. Avoid using wire nuts in RV applications where vibration can cause connections to loosen over time.

Secure all wiring away from heat sources and sharp edges. The area around your new tankless heater will get warm during operation, so make sure wires aren't touching the unit housing or gas lines. Use zip ties or wire loom to organize and protect your connections.

Test the complete installation several times - run hot water for extended periods to ensure the unit cycles properly and maintains temperature. Check that all connections remain secure and that you're not tripping any breakers or blowing fuses during operation.

Call in the Pros

While this wiring identification and connection process is well within DIY capability, there are several situations where bringing in a professional RV technician or electrician makes sense. Knowing when to call for help can save you time, prevent damage to your new Girard II, and ensure your installation meets safety standards.

Consider calling a professional if you discover that none of your existing wires provide clean 12V power, or if the voltage readings are inconsistent or fluctuating significantly. Common causes include problems with your RV's charging system, converter, or main electrical distribution that go beyond the scope of your water heater upgrade. An RV technician can diagnose and repair these underlying electrical issues.

If your testing reveals that you need to run new 12V wiring from your main electrical panel to the water heater compartment, this is another situation where professional help is valuable. Running new circuits in an RV requires understanding of proper wire routing, appropriate breaker sizing, and compliance with RV electrical codes. A professional can ensure the new circuit is installed safely and won't interfere with other systems.

You should also consider professional installation if your RV has a sophisticated energy management system or inverter/charger setup. Some modern RVs have complex electrical systems where adding or modifying loads can affect other components in unexpected ways. An RV electrical specialist can evaluate how your new tankless water heater will interact with your existing systems.

Gas line connections are another area where professional help is often warranted. While you're only dealing with the electrical side of your Girard II installation, if you discover any issues with the gas supply lines, shut-off valves, or venting during your electrical work, these should be addressed by a certified RV technician or propane specialist.

Professional installation typically costs $200-400 for the electrical connections, depending on complexity and whether new circuits need to be run. This investment can be worthwhile if you're uncomfortable with electrical work or if your RV's wiring situation is more complex than a standard installation.

Even if you complete the installation yourself, consider having an RV technician inspect your work, especially if you had to make significant modifications to the existing wiring. They can verify that your connections are secure, properly protected, and that the circuit can safely handle the Girard II's electrical requirements.

Remember that improper electrical connections in RVs can create fire hazards or damage expensive electronic systems. If you have any doubts about your wire identification, voltage readings, or connection methods, it's better to invest in professional help than risk damage to your new tankless water heater or your RV's electrical system. Always ensure all connections are torqued to manufacturer specifications and that you're using the correct parts for your specific model (verify with your dealer).