1989 Volvo 760 Turbo: What is the 2nd connection on positive battery terminal

Just put a new battery in my wife's car the surface voltage was fine but under load it failed . So I turned the lights on and it went down badly. The new orbital battery will sort that out as they have heavy discharge quick recovery . This is the second battery we have bought from Orbital and we are happy . My suggestion is solder up all cables so nothing is loose and make sure the cables are right by giving them a good tug . Check your battery terminals to see they are clean and see if your lights get brighter when you slightly rev your car so then you will know if your battery is charging . Make sure your earth and positive cables are doing their job ,a good earth a good belt and good reading from the alternator is important . And good luck .

My battery is new and the terminals and cables are clean and tightly connected. The lights DO NOT get brighter when I rev the engine, I'm sure the battery is NOT charging.

So,

- does anybody know what the second connection does, the one coming off the positive (red) terminal? and

- Any guess (other than a broken alternator), about possible causes of the problem? Or, tips and hints on how to pinpoint/diagnose the problem.

Thanks, Wolfgang.

Off the top of my head maybe feeds the alternator but without the wiring book i could not be sure