Weird electrical gremlin

Driving home from work today, every time I touched the brake pedal the hicas light came on. At first I thought low fluid and momentum, but it was definantly the electrical connection. In addition my dash lights dimmed as well, also quite often the aftermarket gauges would reboot (fed from stereo ign power and Lx) and a couple of times the stereo rebooted too. 

I got almost home, literally as reversing on to my drive all electrics cut out, like totally (even the electric ariel didn't go down) and stayed dead. 

After about 10 minutes of manouvering it by hand (steering is so heavy when off) back on to the road (so I can use other car tommorow) it just all came back to life (stereo had lost settings so was a complete power loss) 

Anyone got any ideas? 

Don't want to drive it in case it cuts out on motorway, and fault finding is harder now it's working again

I initially thought with the dimming dash lights and gauge reboot a short circuit between the brake lights and ground. But what's that to do with hicas / power stearing? And then with it completely dying I'm confused