What could cause a fault in a 1989 Pintara wagon that causes the speedo and headlights to stop working and the indicators to light up and noise from computer box when turning on highbeam?

Turned out to be a bad earth in the engine compartment. I had degreased the engine and knocked out some of the crud around the earthing point. The earthing wire was subsequently loose. Got an electrical fault? CHECK ALL THE EARTH CONNECTIONS FIRST!!! I had checked all the switches, relays and connectors I could get at before checking the earth connections...