That diagram helps a lot. It appears to be a 24-volt control system, and the important thing is that the Arduino should not be connected directly to the colored solenoid wires.

From the diagram, I see a 24 V constant-power feed (red) going to the switches, with the switches sending that 24 V to the appropriate solenoid/pump wires.

What I think your existing switches are doing

The switches appear to be center-off momentary switches. Conceptually, each one is:

So when you push the switch UP, the common terminal connects to the lift/pump output.

When you push it DOWN, the common terminal connects to the dump output.

When released, neither output is connected to 24 V.

That is actually a very good arrangement for Arduino control because we can make the Arduino electrically imitate those switch contacts.

The Arduino should act like another set of switches

For example, suppose you wanted the Arduino to control the front:

The Arduino would energize the appropriate relay for however long you specify.

For example:

Front UP button pressed once:

Front DOWN button pressed once:

You could make that 1 second, 5 seconds, 10 seconds, 30 seconds, 60 seconds, etc.

But your diagram shows something important

I would not build the Arduino circuit yet, because your diagram appears to have considerably more than the "3 solenoids" you originally mentioned.

I can see these outputs:

• DFR — Dump Front Right
• DFL — Dump Front Left
• DBR — Dump Back Right
• DBL — Dump Back Left
• PF — Pump Front
• PB — Pump/Back

And there are apparently several switches controlling combinations of those outputs.

So the Arduino could potentially give you quite sophisticated control, such as:

Front

Rear

And potentially:

Individual corners

If the existing switches already accomplish these functions, the Arduino can reproduce exactly those same combinations.

I would use relays rather than connecting Arduino pins to the 24 V system

Something like this:

The relay contacts handle the 24 V control circuit.

The Arduino only controls the relay coils.

That gives us isolation between the Arduino's 5 V electronics and the hydraulic system's 24 V wiring.

One very important safety feature

The software should prevent UP and DOWN for the same circuit from being active simultaneously.

For example:

I'd actually go one step further and use electrical interlocking in addition to the Arduino software. That way, a software failure can't accidentally activate lift and dump simultaneously.

Your 24 V system also changes the relay selection

Don't buy a relay board just because it says "Arduino relay module."

We need to know the actual current being switched by each switch circuit.

The relay contacts need to be rated for the voltage and current of the hydraulic control circuit. Since the solenoids are inductive loads, we also need appropriate suppression/protection.

And because this is 24 V, the Arduino's power supply needs to be handled separately — typically a suitable automotive DC-DC converter rather than putting 24 V directly onto the Arduino.

I think the next step should be to map your switches exactly

The image gives me the overall circuit, but I need to know which physical switch terminals correspond to which wires.

If you can take a clear photo of the back of the actual switch panel, showing the terminals and wires, I can help you identify:

1. 24 V common
2. UP/lift contact
3. DOWN/dump contact
4. Which wires are DFR, DFL, DBR, DBL, PF and PB
5. Where the Arduino-controlled relay contacts should be connected
6. How to make a single Arduino button press run the function for a selectable number of seconds
7. How to retain the original manual switches
8. How to prevent simultaneous UP/DOWN commands

If you send me a photo of the back of the switch panel and the individual switches, I can work through the wiring with you before you connect anything.