unplugging becm

Hi guys I want to check is the becm under the passenger seat that being nearside,I have notice there are 3 units under there ones say gearbox ecu one on top of the other at front of seat base then there is another unit at rear of seat base, which one is the becm ?
Is there a correct way to unplug it,or just key out ignition off. I want to check the connections are all clean and maybe some checking for the radio sat nav amp system.
I dont want to risk doing any damage by doing this incorrectly also is it likely to give me any problems by doing this ie having to resett windows and anything else,will it still recognition the key etc,jst want to know as I dont want to give myself any other problems by doing this ? I have a P38 2002 Westminster Diesel with Harmon kardon dsp and sat Nav FYI.

Thanks

Yours is right-hand drive? BECM is under the driver's side (=off side).

Under the passenger seat might be a gearbox ECU and the EAS ECU.

BECM is under the drivers seat.Disconnect battery first, slacken battery negative clamp, switch ignition on and off, disconnect earth from battery within 17 seconds or the alarm will sound.You will have to reset the windows and radio code when you reconnect. Easier to acces the BECM with the seat removed.

As mentioned above. Make sure the vehicle is UNLOCKED when you disconnect the power as you can secure the vehicle manually from the inside on rear doors/front passenger door and with the key in drivers door if you need to lock it up. Disconnecting the power with it locked already can cause a ton of headaches.

With the front seat removed (4x Torx T50 bolts, once the plastic trim is removed) then it's 2x philips head screws on the air duct, a load of connectors, 4x 8 or 10mm captive nuts (on the 3x power and 1x ground connectors - I've seen both 8mm and 10mm nuts used depending on year, bu I think most are 10mm). Then there is 3x 10mm nuts bolting the BECM down onto studs in the bodywork - 2x at the front, and 1x at the rear.

Under the LFH seat, as Grrrrrr mentions is the EAS ECU, Gearbox ECU (for auto models) and the Transfer Case ECU

Thanks guys.