Metalen 12V en 24V drukschakelaars met LED verlichting

Connecting a 12V or 24V switch: choosing power, relay, and fuse

09 Aug, 2026
Posted by: ABC Webshops

When installing additional lighting on a car, bus, tractor, boat or machine, the primary concern is often whether a switch operates at 12V or 24V. While necessary, this alone is not sufficient. The contacts of the switch must also be able to handle the current of the connected load. Additionally, the cable and fuse must be suitable for the same current.

Short answer: First, calculate the current using the formula amperes = watts ÷ volts. Compare this value with the DC specification of the switch. Use a relay when the load is too high for the switch or when you want to keep the heavy power cable short. Install an appropriate fuse close to the power source to protect the cable and installation.

12V and 24V: why does it make a difference?

For the same power output, 12V carries twice as much current as 24V. A 60-watt lamp theoretically uses about 5 amperes at 12V and 2.5 amperes at 24V. Therefore, a switch or cable that seems perfectly adequate at 24V can be subjected to a much heavier load at 12V.

The basic formula is:

current in amperes = power in watts ÷ voltage in volts

For multiple lamps, add up the total power. Two 48-watt lamps together equal 96 watts. This is theoretically 8 amperes at 12V and 4 amperes at 24V. In practice, inrush currents and losses can play a role, so do not choose components precisely at the calculated limit and follow product specifications.

Check the DC load rating of the switch

A switch often displays a maximum current, for example, 10A, 20A, or 35A. Check the voltage and current type for which this value applies. A high AC specification for 230V alternating current should not automatically be interpreted as the same DC load.

Also, check whether the rating applies to a simple resistive load or to the specific application you intend to switch. LED drivers and other electronic devices can draw a higher current briefly upon switching on than during normal operation.

When do you use a relay?

A relay allows a small control current from the dashboard or push-button switch to switch a separate circuit with a higher load. This means the full lamp current does not have to flow through the operating switch and the cable to the dashboard.

A relay is particularly practical when:

the total current is higher than the switch can safely handle;
multiple work lights or a powerful LED bar are switched simultaneously;
the distance between the power source, switch, and lamp is large;
you want to use a compact push-button switch with a limited contact load;
you only use existing vehicle controls as a control signal.

Many vehicle relays use numbered connections, but the design and diagram can vary. Therefore, connect a relay according to the diagram on the product and not solely based on wire color or an online image.

Why is a fuse necessary?

A fuse is primarily there to protect the cable and installation in case of a short circuit or overload. Without adequate protection, a cable can heat up significantly if the insulation is damaged or a connection shorts out.

Place the fuse as close as possible to the point where the power cable connects to the battery or power source. The fuse rating must match the cable, load, and regulations of the connected equipment. Do not simply choose the largest fuse to prevent it from blowing; this could leave the cable insufficiently protected.

What cable thickness do you need?

The required cable cross-section depends on the current, cable length, permissible voltage drop, ambient temperature, and how the cable is laid. A longer cable has more resistance for the same cross-section. This can result in the lamp receiving less voltage and the cable heating up more.

Calculate the entire current path, there and back, and use a cable table suitable for 12V or 24V vehicle installations. When in doubt, a larger cable cross-section is often beneficial for voltage drop, but connectors, terminals, and the fuse holder must also be able to accommodate that cable properly.

Illuminated switches: pay attention to the extra connection

An illuminated switch can have two different functions. The light can turn on when the switch is active, or it can serve as backlighting that illuminates with the vehicle's lighting. This means some switches have three or more connections.

Check which contact is the input, switched output, and ground for the indicator LED. An incorrectly connected indicator light can stay on continuously, not work, or cause the load to react differently than expected.