You want the LED in your push-button to follow the equipment it controls: load ON, LED ON; load OFF, LED OFF. The simplest wiring is to take the LED positive feed directly from the switched output going to the load. It is clean, intuitive and usually avoids another relay or a separate status circuit.

There is one electrical detail to understand first: motors, relay coils and solenoids are inductive loads. When their current is interrupted, they can generate a short reverse-voltage pulse called back-EMF. That pulse can be much harsher on a small LED circuit than the normal 12V supply.

Why does an inductive load create a voltage spike?

A coil or motor winding stores energy in its magnetic field while current is flowing. When the switch opens, the current cannot disappear instantaneously. The collapsing magnetic field generates a voltage that tries to keep the current moving.

In a positive-switched 12V circuit, that transient can drive the switched output below ground for a brief moment. If the LED is connected between that switched output and ground, it can be exposed to reverse voltage it was never designed to tolerate.

Which marine loads are inductive?

Typical examples include bilge pumps, pressure pumps, blowers, wiper motors, hydraulic pump motors, standard 12V relays, contactors, solenoid valves, horn solenoids, electromagnetic clutches and similar actuators.

The important question is not only the equipment name, but which inductive element you are suppressing. A 350A windlass contactor may switch hundreds of amps through its main contacts while its control coil draws only a fraction of an amp.

Option 1 — Use a 1N4007 flyback diode

For an ordinary one-direction 12V relay coil or small solenoid, a 1N4007 can be connected directly across the inductive component.

The diode is installed reverse-biased during normal operation, so it carries no current while the equipment is energized. When the supply is removed and the coil tries to reverse the voltage, the diode becomes forward-biased and gives the remaining current a safe local path.

Where should the diode go?

As a general engineering rule, suppress the transient as close as practical to the inductive component generating it. That keeps the current loop short and prevents the transient from travelling unnecessarily through the rest of the harness.

For a relay coil, that means across pins 85 and 86. For a small solenoid, it means across the solenoid terminals. If the equipment already includes internal suppression, follow the manufacturer's wiring instructions.

Option 2 — Use a relay with the suppression diode built in

In most 12V marine panels, smaller accessories can be switched directly by a suitably rated push-button. Once the required current rises beyond what the switch should carry, the normal architecture becomes:

The push-button is then only energizing the relay or contactor coil. A relay with an integrated flyback diode makes the installation cleaner because the suppression is already connected directly across that coil.

Because the diode has a defined polarity, diode-protected relays are polarity-sensitive. Always respect the manufacturer's coil polarity. In many automotive-style relays, pin 86 is positive and pin 85 is ground, but verify the actual relay before wiring it.

Can I use a 1N4007 for everything below 20A?

No. The main load current is not automatically the current that the flyback diode has to handle.

A 1N4007 is a very good choice for many ordinary relay coils and small solenoids because those coils generally draw far less than 1A. A 12V motor drawing 10A or 20A is different: immediately after switch-off, its suppression path may initially have to carry approximately the motor winding current.

Why reversing motors need special treatment

A standard flyback diode assumes the polarity across the load always stays the same. Windlasses, bow thrusters, trim pumps and other reversing systems intentionally swap motor polarity. A diode that is safely reverse-biased in one direction can become a direct short circuit when polarity is reversed.

For those systems, use the suppression method specified by the motor or controller manufacturer, or a properly engineered bidirectional transient solution such as a suitable TVS arrangement.

What this means for the push-button LED

If the LED is connected to the switched output, the cleanest approach is not to ask the LED to survive the transient. Prevent the transient from developing at the source. Once the inductive load or control coil is correctly suppressed, the same switched output becomes a much friendlier signal for the LED.

Troubleshooting an LED that keeps failing

• Identify whether the controlled device contains a motor, relay coil or solenoid.
• Check whether that device already includes internal suppression.
• Confirm where the LED gets its positive feed.
• Check whether a flyback diode or other transient suppressor is installed.
• Verify diode polarity: cathode stripe toward positive.
• Confirm whether the load reverses polarity.
• For motors, verify that the suppression device is sized for the actual motor circuit.

The short version

The objective is simple: keep the inductive energy where it belongs, prevent it from travelling back through the control wiring, and let the push-button LED indicate load status without becoming the weakest component in the circuit.