The conversion is really not too difficult. None of the wires need to be replaced for a successful conversion because the amount of current required for a 12-volt system is 1/2 the current required for a 6-volt system.
Start by verifying that a 12-volt battery is installed. If so, and the engine starts and runs, the coil and power to the coil has been converted properly. When the engine starts, does the ammeter jump to the positive side of neutral? Does the battery remain charged? If so, the generator/alternator has been converted correctly.
Check all your lights. All of the lights need to be replaced with 12-volt lights. If the lights work, they were already exchanged.
The fuel gauge is the only instrument you need to worry about. The water temperature and oil pressure gauges don't use electricity, and the ammeter doesn't care what voltage is used. The fuel gauge needs to be replaced with a 12-volt version, or you need to install a special resistor near the gauge. If you have a heater motor in the truck it needs to be converted to 12-volt or a resistor needs to be installed in the circuit. That's about it. You can use an inexpensive volt-meter to check voltage at each of your devices if you want. I gave you the short story. There are hundreds of posts on this topic in the forum. If you do a search, you will find lots of detailed information.
