2006 Central locking query

Hello everyone! 

I have a JB43 Jimny with a very weird and mildly infuriating problem. The Central locking is intermittent, half the time it works and the other half it doesn't. The weird issue is that once the key is inserted into the ignition (not turned to accessory or on position) it begins working as it should.

Things I've tried: 

• Pulled the door card and sprayed contact cleaner in the motor connection and gave it a few wiggles
• Ensured that the motor was receiving constant power
• Checked with the service manual to ensure wiring is correct and had not been tampered with in the past (I only checked the motor wiring, not sure where the wires go after they pass through the door) 

it's very strange that once the key is inserted it begins to work normally, any ideas? I'd like to install a remote central locking system but need to sort this out first!

Thanks for reading and helping out!!

Any difference in the response when you turn the key in the door lock, push the button at the drivers door, or pull the knob at the window sill?
I Think mine Has Some sort of blocking when lights are left on, or the Doors is not shut properly.

I've tested using both keys.. both doors locked (all lights off) and manually using the pull knob. Only operable when key in ignition. Just can't wrap my head around why it works when key is simply put in the ignition

Thanks for the suggestion Lambert, i pulled out said module, bridged 2 pins to give it constant power, only thing is the beeper wouldnt stop beeping even with doors closed so i just cut it out. Central locking works a charm now  . 

I would then also check the electricity consumption. If the beeper beeps all the time maybe some module does not go to sleep and slowly drains your battery and after two weeks it might not start.