You can use either dark or light soy. If you cannot find the pimento peppers, you can use a 1/4 scotch bonnet or habanero pepper finely diced.
You can add some apple wood to the coals for a fruit smoky flavor, which will compliment the pork well. If you do not have a charcoal grill a propane grill can also be used.
You must first marinate the pork tenderloins. In a bowl combine the soy sauce, ginger, garlic and brown sugar, place tenderloins (washed and dried) in Ziploc bag (something strong so it doesn't leak) and mix the ingredients. Seal the bag, massage meat then put in a bowl in the fridge. The bowl is in the case of leakage. For extreme flavor allow meat to marinate over night.
While your meat is marinating you can get you coals up to temperature. Discard marinade. Allow meat to sit at room temperature before placing on a hot bbq.
I use the indirect method where I place the tenderloins away fro direct heat and allow to slowly cook for about 45 minutes. Always keep the skinny end of the pork away from the direct heat. It ALWAYS cooks faster and can dry up on you.
When removing the tenderloins from the bbq, it is important to cover the tenderloins in some tin foil and allow them to rest before slicing.