I wired an alarm a few weeks ago, its wired into ignition wire only.
I had disconnected the main loom to engine loom plug looking at splicing to the ignition there but was going to be too much of a pain wiring back into the cab so spliced under the dash for ignition cut.. reconnected plug.

I dropped the fuse panel down for ease of access and put multimeter on just to check correct wiring for ignition on and battery power. When I put multimeter on all power went out. Thought perhaps an issue with the plug I had played with earlier so disconnected and checked and reconnected all power back.
Multimeter again on fuse panel and all power back out... disconnect and reconnect plug again and power back. Figured i was making a short at the fuse panel and must need to be earthed to body so screwed back in and no further dramas checking things.

Went to drive car this morning started andxwarmed about 5 mins.. went to move, all power out. Disconnect and reconnect plug all back on.
Whats tripping and Im resetting it by cutting power when that plugs disconnected? Cant see any relay in wiring diagram?