If it's a 2 speed motor then it will have two independent sets of windings. That would naturally have 6 leads. The fact that yours has 12 leads me to believe it has a high/low voltage option as well. Pairs will be wired in series or parallel depending on input voltage. Identify the windings for the high speed and connect those to your VFD. Tape off the remaining connections.

A picture of the nameplate will get you a more accurate answer.

How could I identify either of the speeds? For delta I’ll just need to connect the end of one to the end of another power it, other end connected to another pair end, power it and so on?

The information you need is typically on the nameplate of the motor or on the inside of the cover for the junction box.

Is the motor still connected to the multi-pole switch? Find the 3 leads connected to the high speed terminals on the multi-pole switch. Those are the 3 leads you need to connect to your VFD.

There was 6 connections going to the multipole switch

The motor does not appear to be 2 speed or dual voltage from the nameplate. That is strange.

Some people will use the 12 lead configuration to indirectly attain 2 speeds, by using a Wye-Delta or Part Winding arrangement but not solely as a starting scheme, they leave it in the first stage as the low. So really it is two TORQUES, then the load determines the speed that it runs at with the lower torque. This however only works with centrifugal machines like pumps and fans.

To use it with a VFD, just connect it for the voltage that you are running at, the VFD will take care of the rest (with proper programming of course).

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

With all the terminals unmarked in the motor cap, how could I identify which is which? I can tell with my ohm meter which ones pair up but I’m left with 6 pairs. Which ones would go together ?

Is the motor still connected to the multi-switch?

With 1:2 speed, it's a Dahlander winding as below.

Delta is low speed (supply at 1U 1V 1W and 2U 2V 2W open).

Two Wye is high speed (supply at 2U 2V 2W and 1U 1V 1W shorted).

Tricky part is identifying the leads if they are not marked.

Muthu
www.edison.co.in

TugboatEng it’s not connected to the switch at the moment but I have marked where all the cables were connected to.

Edison123 if I was to connect it in a fashion which I think is delta according to your diagram, if it was wrong would it not spin at all? I can try it on a true 3 phase supply as I’m dubious about connecting it to the VFD if I’ve got it wrong

Since you have marked the leads, restore the original connections to the multi speed switch, apply direct voltage without VFD as before to check the both the speeds and then insert the VFD between the supply and the switch.

Muthu
www.edison.co.in

Your nameplate shows only 2 poles.
Probably the motor has two independent windings and that the second nameplate is missing.

How to get more efficiency

I haven’t got 3 phase here also I need to wire it in delta before the single to 3 phase inverter will work

Quote (I need to wire it in delta)

Then you need to take it to a winding shop where they will most likely suggest to rewind it for your speed and connection since it a major pita to sort out 12 unmarked leads. Or buy a new motor for your specs.

Muthu
www.edison.co.in

Quote (I haven’t got 3 phase here also I need to wire it in delta before the single to 3 phase inverter will work )

Actually you don't.
There is no way to tell if a motor is internally connected wye or delta from the supply wires. The inverter cannot tell a wye motor from a delta motor.
I once had to connect a consequent pole (Dahlander) motor with all the markings missing.
I removed the rotor and with a battery and a compass I identified each winding location and polarity by energizing a winding and then finding the physical location and polarity with the compass.
What is your supply voltage?

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Ohm's law
Not just a good idea;
It's the LAW!