mystery said:

there would be a tiny printed circuit board holding the motor and possible the latch micro switch in the lock mechanism ,the CEM would be a partial printed circuit board containing the Field effect transistors and relays .
Try running ground from negative terminal of battery to pin 2 and 3 then latch the lock closed press tailgate open on switch and see if you get 12 volt on terminal 1 and that the lock opens . I would also check the loom where it enters the tailgate and the body for damaged or broken cables

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Hi again. I will try this maybe not until tomorrow as I have sheep to move around today Please tell me, why is it called a "motor" when surly it is a solenoid? Thanks Ken

because it's a motor and gearing I do believe the repair kits contain a gear wheel etc https://www.ebay.co.uk/itm/386837594653

Hi again.

I have not opened up the CEM but have disconnected the 8 pin connector to the latch. I have measure the resistance across terminal 1 and 2 and for this unit I get 5 ohms. Naturally with the latch closed, I have connected a 12volt supply across terminals 1 and 2 (+ to terminal 1) The latch does not open. I have a 2.5A stable power supply which as you would agree should be enough power for a resistance of 5 ohms. But my power supply registered “over load” so it would seem it could do with more power to operate – your 5 amps again.

I do not have an isolated 5A supply by could take a fused line off the battery – I have a 12V supply on the left had side of the back door (I assume that all Fl2 do!) but do not know what the fuse rating of this is off hand?

I am thinking that, as both the old and the new latch do not open when supplied with 12volts, that the 3rd wire need to be involved?

The pins on the latch are very close together so it is difficult to play around with the terminal. Do you know the type of connector used on this – if so I could order one on Ebay.

I'm not sure if the motor is controlled by PWM (pulse width modulation) if so this would put the control voltage signal at 5volt halfwave but going by the diagram i would say this is not the case . so with the motor disconnected ground the terminals 2 and 3(this will eliminate a faulty lock micro switch ) and actuate the tailgate via the remote or open button on the tailgate whilst measuring the voltage on terminal 3