How to connect the battery to the alternator on a 1973 aermacchi Z90 motorcycle

Technically you can't. A battery is direct current DC and an alternator is alternating current AC. You need to connect a rectifier to the alternator output wires this converts AC to DC then you will need some form of regulator to make sure the current does not overload the electrical system. Most modern bikes have the rectifier and regulator in one unit. Older bikes often had/have 2 units to cover this.

The Z-90 takes a 6-volt battery. I don't know the size of it. Since its not an electric start, you can put a gel cell battery in it. For a service manual and parts manual, contact Leslie at MotoItalia in California. http://www.motomacchi.com/

Good Luck
Steve

if you know its location trace wire harness up to the first disconnect and read into the plug, there should only be three pins, measure the resistance of any two pins in any combination and they should all read less than 1 ohm, if any one of the three winding read open, or high resistance, then its bad, and will need to be replaced. usually its not the alternator that causes the charging problem, its the regulator. Your battery has to be in good condition to start with... so it can accept a charge..it might have a bad cell in it..battery voltage static, should be minimum 12.4 volts..12.6-to 12.7v nominal. if your battery reads 11 to 12.0v and is over two years old, its probably bad. Can i get a ratting if this helped you, thanks!

ss 350 aermacchi?There are many on-line salvage parts dealers that will have what you need. this is just one example. http://www.classiccycleparts.com/ ,