This happened occasionally over the years, but now regular.

Mazda 626 93 V6.
Factory 2096 alarm box under the dash (power lock disconnected).
Wipac EP10 immobiliser.

Turn key.
Click-k-k-k-k-k under dash, whole car goes dead, no starter sound.
No headlights, no door lights, no by sunroof push-light, everything
DEAD.
Wait a minute.
Suddenly door lights return, Wipac re-arms (as if power returns).

Turn key.
Starts fine - except the past week it has not.

Disconnected the car battery, unplugged the factory alarm "2096" box
under the dash, but I am not getting a clear cause and effect. Nothing
works until suddenly it will start as normal.

That the car goes "dead" and comes back with the Wipac immobiliser re-
arming suggests the voltage dropped out. The battery was replaced
after the bad winter 2 months ago. Battery 12.92V after just shutting
off tonight, restarted it 3 times without problem.

Anyone recognise this?

Is this a bad main relay or the factory alarm?
Why would everything go dead then come back after about a minute? The
Wipac immobiliser is reliable & well fitted, the factory alarm is
original and is known to give current drains (hence the door lock link
is unplugged).