Yaris 2005 sudden electrical failure

[sceh]

Twice I have been driving and suddenly the steering is heavy, the engine light comes on, the gearbox light may come on andI roll to s stop . The engine continues to run and I can then drive off within a few seconds. Today when I put the hazard warning lights on they didn't light immediately and I did hear some odd clicks under the bonnet.
So, it looks like a complete but temporary electrical failure. Where do I start to find out why? Note that the engine keeps running too.

Thanks for any help