Okay, Doug, welcome! This is a common and frustrating problem. The most likely cause is capacitive coupling or inductive coupling. Here's a breakdown of why and what to check

Understanding the Problem: Capacitive/Inductive Coupling (Ghost Voltage)
Capacitive Coupling

Wires running close together act like capacitors. The energized wire (carrying the 120VAC to M136 when the switch is closed) can capacitively couple some voltage onto the adjacent de-energized wire (wire 42). Since you are measuring with a high impedance meter, it requires very little current to get a voltage reading. You have a voltage, but with almost no current behind it.

Inductive Coupling

A similar effect, but instead of capacitance, a magnetic field from the energized wire induces a voltage on the adjacent wire.

Why you don't see it to Neutral

Ground is typically a larger reference, and more sensitive to picking up capacitive and inductive noise. Neutral is a closer circuit reference to the hot conductor and any stray voltages tend to reference to ground.

Troubleshooting Steps1. Confirm Meter Impedance

Crucially, you need to know the input impedance of your multimeter. A digital multimeter (DMM) typically has a very high impedance (1 MΩ or 10 MΩ or more). This is exactly what makes you see the ghost voltage. An older analog multimeter (with a needle) typically has a lower impedance and will "load down" the circuit, causing the ghost voltage to disappear. If you have access to an old analog meter, try that. If the voltage disappears with the analog meter, it strongly suggests capacitive/inductive coupling.2.

Load the Circuit (MOST IMPORTANT)



The key test is to put a load on the circuit. Find a resistor (something in the 1k ohm to 10k ohm range with a wattage rating appropriate for 120V - so at least 2 watts) and connect it between wire 42 and ground with SS136 open. If the 120VAC reading drops significantly (to near zero) when you connect the resistor, that confirms it's a ghost voltage. If the voltage stays at or near 120VAC with the load, you have a more serious problem (a short or miswiring).3. Check for Shorts or Miswiring

This is less likely if the voltage disappears when the resistor is applied, but still important to rule out. With SS136 open and the power OFF, use an ohmmeter to check for continuity between wire 42 and the 120VAC supply line (L1). There should be no continuity. Also, check for continuity between wire 42 and ground. Again, there should be no continuity.4.

Wire Routing

Look closely at how the wires are run. Are wire 42 and the 120VAC supply wire running parallel and close together for a long distance? If so, this increases capacitive/inductive coupling. Try to separate them as much as possible. You may need to reroute wires. Are any wires pinched or damaged? This could cause a slight short allowing the voltage to bleed through5.

Relay Leakage (Less Likely)

While less likely, it's possible there's some leakage through the relay (CR236). This would be more likely if the relay were old or damaged. Remove wire 41 from the relay (CR236) output. If the voltage on wire 42 goes away, the problem could be the relay.6.

Neutral/Ground Issues (Important for Safety)

This is unrelated to the ghost voltage, but very important. You mentioned not seeing 120VAC to Neutral.

Verify that your neutral and ground are properly bonded in your electrical panel and that there is no excessive voltage between neutral and ground. A high neutral-ground voltage can cause all sorts of weird problems and is a safety hazard. With no load on the system, the voltage between neutral and ground should be very low. Ideally less than 2-3 volts. Call a qualified electrician to verify ground/neutral is good if you are not familiar with thisImportant Notes



Safety First

Always disconnect power before doing any wiring checks. Be careful when working with 120VAC.

High Impedance Meters

Modern DMMs are great for most things, but their high impedance can make troubleshooting these types of ghost voltages tricky. The high impedance makes it easy to pick up these small "stray" voltages.

Don't Ignore It: While a ghost voltage isn't usually dangerous, it can* cause problems with sensitive electronics. You should address the underlying cause (wire routing, etc.) to minimize it.Let me know what you find with the load test and any of the other checks. Good luck! Flag for review