Hilux Alternator Modification
Try the following. Start the engine and have it run at idle. Switch on all healights, spot lights, radio etc to draw as much power possible.
Now test the voltage on the battery. You should have in the region of 13.8v. If you don’t get this, stop the engine and disconnect the battery.
Find a long enough piece of thick electical wire (welding cable would be perfect) and connect the possitive out on the alternator to the possitive on the battery.
Connect the battery again and start the engine. Test the voltage on the battery and see if it has improved. If you still don’t get close to 13.8v (remember to switch on all the electrical stuff in the vehicle before testing) you might need to modify the voltage regulator. Take one of the cheapies to test the modification with.
Before you start, you will need to buy a diode from an electronics shop (1N4007). Cut the one leg of the regulator and replace the cut part with the diode making sure it is connected exactly like the one in my pic
After reinstalling the regulator and alternator into the bakkie do the idle test again. You should now get a charging voltage in the region of 13.8v to 14.7v
PS: You can read more here...