1993 Other Toyota Models Electrical problem

Electrical problem
1993 Other Toyota Models Automatic 73,000 miles

Hey, I have a Toyota townace and the problem is when I engaged the car's electrics/spark plugs I get this buzzing, groaning kind of sound from the engine.

I've narrowed the sound down a small piece that looks like to feeds to the battery. If has 3 wires running from it and this is where I suspect the problem is.

can anybody suggest any ideas please?

Paul.