I accidentally shorted the battery on my 94 EF Falcon Auto XR6 Station Wagon while I was fumbling around in the dark Now it won't start, the starter motor turns but the car won't fire. I've noticed the Smartlock light has stopped working on the dash, and the locks no longer respond to the keyless remote (but they respond fine to the key though), so it looks like I've immobilised the car by cutting power to the Smartlock module. On further investigation the power windows, radio, interior lights also do not work, and I can't hear the rear demister relay click when I push the button. I have done the obvious things like replace all the relays and fuses in the engine compartment and behind the removal panel in front of the drivers knee, but to no avail, I can't get any of these items to work!...so now wondering if all these items are feed power via the same source and I've blown something on this circuit!...Any ideas?? (apart from the fact I'm clumsy idiot!! )

double check on your fuses and put a multimeter on the fuses u have installed. had this happen put in a fuse be like hmm why no working!!! bu went back over and was fuses.

Double check the main fuse in the engine bay.
A dead giveaway is the ODO display wont illuminate.

hhhmmm.....my ODO is illuminating as normal!...(don't know whether thats a good sign or a bad sign now!!! )...I will triple check all the obvious fuses again, let me know if u have any other ideas, any help is much appreciated as I'm in the UK so the car workings are pretty unknown out here!

All of the things that you mention are not working (power windows, interior light, remote, demister, smartlock) all run off the BEM to run their appropriate relays. It sounds like your BEM is not getting power.
Check your CRT LP (interior light) fuse under the dash. This will cause a car to act as if it is smartlock immobilised.

Replace your courtesy lamp fuse in the fuse box with a brand new one (even if the existing one looks ok) and see if that fixes the issue. Whenever I'm working on the stereo or the interior of the car I always pull the fuse for that circuit, partly to stop the lamps from being constantly on, partly so that if the other half tries to borrow the fairmont instead of taking her excel (she prefers my car to hers lol) the car will turn over but not start. Then again, the downside is you lose all the settings like lamp brightness level, stereo memory etc.

If the CRT LP fuse replacement doesn't fix the issue, then I would start troubleshooting the BEM.

Just my thoughts, comments and opinions. Cheers

did the same to an EF.

if the CRT fuse (RED 10AMP FUSE) is blown u will have these symptons :

Central locking remote wont work (dead give away theres a problem with the smart lock)

Headunit wont work.

no interior lights

no boot light

car will start but not turn over.

cheers

Mate ,,If you didn't live on the other side of OZ you would be getting a MANHUG right now. You fixed my problem . A 10a fuse . Thanks mate .