flickering speedo lights then all warning lights illuminate and cut out?

Hi On the way back from MOT I noticed the speedo light doing a very small flicker not all the time but enough to notice. Then all at once, all the warning lights illuminated and the headlights went out and back on again. The engine stopped but refired, I took it easy and managed to get home. I noticed today That the reverse lights don't seem to operate all the time. I also found that after it had its funny five minutes the car wouldn't lock by the plip, but after manually locking it, it did unlock with the plip after 10 minutes or so.
I have recently removed both the front and rear subframes and replaced the gearbox. I suppose the gearbox reverse switch might be playing up but would that cause everything else to freak out? I don't know if it's only when the lights are on this happens but I did try to get a code reader on but it failed to connect to the car.
Any help would be appreciated, mechanically I'm reasonable, electronically I do lack a bit.

Trev.

Check the wiring loom at the boot lid hinge, the insulation can break, there by causing a short in the lighting circuit.
and check the wiring loom running along the leftside inner front mudgaurd/wing/fender( use whichever word is appropriate for your part of the world) I had shorted out wiring here.

I would be checking the main body earth leads.

Would that be the one from the rear subframe to the body by the80amp fuse. If so gave that a sand down today see how it goes.

Also the one from the inner wing to the battery.