An alternator is an electrical device which generates alternating current by changing mechanical energy to electrical energy. Alternators are cheaper and easy to find compared to their counterparts -- the generators -- and therefore more preferred in vehicles. Conversion from a generator to an alternator is a task that requires the vehicle to change from positive to negative ground as an alternator will never work on a positive ground state.
Switch off the engine of your vehicle and disconnect the clips of both the negative and positive terminals of the car battery. Turn the vehicle battery 180 degrees and connect the cable leading to the starter to the positive terminal of the battery under positive to negative ground conversion. Do not connect the negative terminal as you will have completed a circuit and electrical accidents are bound to occur.
Remove the cover of the dashboard to get to the ammeter. Reverse the wires on the back side of the ammeter using a screw driver to connect the negative to positive terminal and vice versa.
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Disconnect the wires connecting the tachometer (revolution counter) and remove it completely from the dashboard. Take the negatively ground tachometer and place it at the place where you had initially removed the other tachometer reattaching all the wires.
Reverse the connections on the ignition coil as this helps in preserving energy in the coil. The ignition coils terminals are usually marked with SW for switch and CB for contact breaker and hence will not be difficult to locate.
Disconnect the generator using the screwdriver and wrench and remove it from its place of attachment. The alternator has a shorter length than the bracket of the engine and therefore inclusion of a metal tube equal to the difference in length between engine bracket and length of the alternator is mandatory to make the alternator fit in place. Fix the alternator and the metal tube tightly using bolts and perform the connections on the alternator exactly how they were on the generator. Remove the old belt of the generator and install it with the new one as the alternator pulley is generally smaller.
Check again to verify everything is switched off. Upon completing the check up, reconnect the negative terminal of the car battery and switch on the ignition switch to verify everything is in order.