The 12 v side ampere rating is unnecessary information (You need 5 watts output power, so if the input is 12 volts, you need around 1/2A input current). Use a DC to DC converter. I found an IC made for this purpose at Radio Shack several years ago - I assume they are still available if you are a hobbyist. Otherwise you can buy premade ones (search for 12v to 5v converter).
You should use ULN2003 or LM398 driver for it
A switching regulator, a DC-AC-DC converter, a motor/generator set, etc.
You have your own answer. It is 1.5 amps.
Change the trailer light bulbs to 24 volts and supply a 24 volt source to power them, in that order.
No Let's look at the current. The current can be calculated in two easy ways using these known data: Volts/Ohms and Watts/Volts Now 12/18 isn't the same as 5/12, so there's something wrong here.
By using a step down transformer.
12 volts, 12 amps
If it is AC voltages you need to convert, you need to find a transformer to do this job. Without knowing the application it is hard to guess what you are trying to do.
5000 volts
+3.3 volts +5 volts, +12 volts -12 volts, and -5 volts but -5 is rare
Volts cannot be converted to amps. If you mean convert 220v to 12 volts output, then you need a 220v to 12 v step down transformer with the VA or watt rating you require.
To what?
You have your own answer. It is 1.5 amps.
If it is AC then you don't need a formula, you just need a transformer.
2 volts, 5 volts, 12 volts. New computers need even less voltage.
12 volts with the engine off. 13.5 to 15-5 volts with the engine idling.
Change the trailer light bulbs to 24 volts and supply a 24 volt source to power them, in that order.
12 volts
No Let's look at the current. The current can be calculated in two easy ways using these known data: Volts/Ohms and Watts/Volts Now 12/18 isn't the same as 5/12, so there's something wrong here.