Okay, you're definitely not a chump. This is a classic problem and can be tricky to diagnose. Here's a breakdown of potential causes, troubleshooting steps, and considerations for your situation

Understanding the Problem: Phantom Voltage/Current

That dim glow when the switch is off is due to a combination of capacitive coupling, inductive coupling, and potentially a real, albeit small, current leakage. Digital multimeters are very sensitive and can pick up these small voltages that wouldn't affect older analog meters as much. Here's a breakdown of the phenomena involved: Capacitive Coupling

Wires running parallel to each other (especially in the same conduit or bundled together) create a capacitor-like effect. The energized hot wire capacitively couples voltage onto the neutral and/or switch leg wire, even when the circuit is open. This is more pronounced with long runs of wire.

Inductive Coupling

Similar to capacitive coupling, but involving magnetic fields. A current-carrying wire induces a small current in a nearby wire, again without direct electrical connection.

Current Leakage

This is the most concerning issue. It can come from a variety of factors:

Compromised Insulation

Older wiring (especially knob and tube), even when replaced, might have sections where the insulation is degraded. Moisture and dust can exacerbate this.

Shared Neutral (Multi-Wire Branch Circuits)

If this circuit shares a neutral with other circuits, current from those other circuits can create a voltage drop along the neutral conductor, leading to a voltage difference between your disconnected switch leg and ground.

Appliances with Power Supplies

Many modern appliances and electronics (even when "off") draw a tiny amount of current due to standby power supplies. This can contribute to the voltage on the neutral.

Improper Wiring

As you suspected, improper wiring like neutrals connected to grounds or grounds not connected together can create current pathways that shouldn't exist.

Troubleshooting Steps & Analysis of Your Situation


Confirm the Obvious First (Again)



Turn OFF the Breaker

The most important step is to turn off the circuit breaker so you are working with power safely.

Verify No Voltage with an Alternate Meter

Use an analog voltmeter or a low-impedance digital multimeter (if you have one) to confirm the voltage reading. These meters will load the circuit more, and if the voltage disappears, it's more likely capacitive/inductive coupling. If the voltage remains, you have current leakage.

Check Breaker Neutral Connections

At the breaker panel, ensure the neutral wire from this circuit is properly landed on the neutral bar and is tight. Look for signs of corrosion or overheating.2.

Isolate and Conquer



Turn off every other breaker in the house. See if it makes the 6 volts disappear from the switch leg. If so, start turning them on again one at a time until the phantom voltage comes back. This tells you what circuit is causing it. It may be a GFCI, appliance, or other lighting circuit. Disconnect the Neutral at the Fixture

With the breaker OFF, disconnect the neutral wire at the problem light fixture. Turn the breaker back on BRIEFLY. Now measure the voltage between the switch leg and ground.

If the voltage goes away

The issue is likely on the neutral side of the circuit. You're getting a neutral voltage difference from a shared neutral or other problem, which is back-feeding to the switch leg through the light bulb filament.

If the voltage remains

The problem is likely on the hot side of the circuit, possibly due to inductive or capacitive coupling or (more seriously) a small current leak between the hot wire and the switch leg due to compromised insulation.

Disconnect the Fixture Entirely

Disconnect both the hot and neutral wires at the fixture (with the breaker OFF). Turn the breaker back on briefly. Measure the voltage between the switch leg and ground at the switch location.

If the voltage disappears

The issue is in the fixture itself (less likely, but possible).

If the voltage remains

The problem is in the wiring between the breaker panel and the fixture location.3.

Focus on the Neutral

Your suspicion of a floating neutral is valid.

Neutral-to-Ground Voltage

Measure the voltage between the neutral bar in your breaker panel and a known good ground (like the metal box of the panel, not the ground bar). This should ideally be close to 0V. If it's significantly higher (over 1-2V), you likely have a neutral problem.

Check Neutral Connections

Carefully inspect all neutral connections in the circuit, from the breaker panel to the fixture. Look for loose connections, corrosion, or signs of overheating.4.

Address the Suspect Wiring



Correct the Obvious Problems

Fix the neutrals landed on the ground bar and any other obvious wiring errors you've found.

Knob and Tube Confirmation

You're right to suspect remaining knob and tube. It's notoriously difficult to completely remove it all. If you suspect it's still present, very carefully trace the circuit's wiring in the attic. Look for: Porcelain insulators (the "knobs") Cloth-covered wiring Open splices (splices not inside a junction box) Any signs of old wiring mixed with newer Romex.

Insulation Resistance Test (Megger)

If you're comfortable using a megohmmeter (megger), you can test the insulation resistance of the wiring. This will help identify sections with compromised insulation that might be leaking current. This requires disconnecting the wiring from the breaker and fixture and is best left to a qualified electrician.

Important Considerations



Safety First

Always work with the power OFF. Use a non-contact voltage tester to confirm the circuit is de-energized before touching any wires.

GFCI Protection

If you're working with older wiring, especially if you suspect knob and tube, consider adding GFCI protection to the circuit. This can help prevent shocks and reduce the risk of fire.

Shared Neutral/Multi-Wire Branch Circuits

Be absolutely certain you understand how this circuit is wired. If it shares a neutral with other circuits (a multi-wire branch circuit), diagnosing problems becomes significantly more complex.

Homeowner Wiring

Given the state of the wiring you've found, it's highly recommended to have a qualified electrician inspect the entire electrical system. Improper wiring can create dangerous conditions.

Halogen Bulbs

The homeowner using halogen bulbs to mask the problem is not* a solution. It's simply drawing more current, which could overload the circuit or mask a more serious issue.

Why This Might Be Happening with Romex

Even if the knob and tube was mostly replaced with Romex, the presence of old wiring nearby can still contribute to capacitive and inductive coupling. Additionally, poor workmanship when installing the Romex (e.g., loose connections, damaged insulation) can exacerbate the problem.

What to Tell the Homeowner

Explain that you've found a potential wiring issue that requires further investigation. Highlight the areas of concern (neutrals on the ground bar, loose connections, potential remaining knob and tube) and recommend a comprehensive electrical inspection by a licensed electrician. Emphasize the importance of safety and preventing potential fire hazards.

In summary:

Don't feel like a chump. Electrical troubleshooting can be tricky, especially when dealing with legacy wiring and DIY modifications. By systematically isolating the problem, focusing on the neutral, and addressing any suspect wiring, you'll be well on your way to finding the solution. Flag for review